The M11 starts in either London or Cambridge, depending on your point of view, but since it was built out from London, let's start from there.
The motorway actually begins in two places, essentially being long slip roads which join together to form the M11. These two slip roads join on to the North Circular, one for people travelling westish and the other for people going east-ish or into the city. The east fork goes right down to London City Airport so the M11 is the motorway of choice for two of London's airports (see Stansted, later).
Small tribute is paid to suburbia as there are few junctions before you reach the M25, and these have restrictions. In fact, I think there may only be one junction, around Loughton. The M25 junction is just a typical two-motorway intersection. In both directions the M11 loses a lane before, and regains it after the intersection. If you want to take the M25 west, make sure you don't accidently take it east/south as you will turn on to the longest stretch of motorway in the country without a junction. This is probably as a result of government planners having an anti-Essex bias.
After the M25 it's just a few miles to The Harlow turn-off (Junction 7). Exciting landmarks around here include North Weald airfield to the right (assuming you are travelling north) and, if you are travelling south, as you reach the crest of a hill between Junction 7 and the M25 you might get a nice view of the Canary Wharf Tower some miles away.
The next junction is somewhat isolated, being at least 10 miles away from the junctions either side. It is where you would be advised to get off for Stansted Airport and Bishops Stortford, that being where these things are located. Also junction 8 contains the only service station on the motorway which, like the M40, ended many years of being service station free a few years ago.
Junction 8 used to be the end of the motorway for a while after it was built and when they extended it to Cambridge they only built two lanes, which was a bit mean of them.
The rest of the motorway is particularly dull as we descend in to East Anglian flatness. Junction 9 (for Saffron Walden and the A11) has some restriction. I think you aren't allowed to leave going south. The next junction is in the middle of nowhere but takes you to Duxford airfield where you can visit some old planes including a concord prototype, if that's your cup of tea. Then that's about it until Cambridge. Actually, I think there are about 4 or 5 exits signposted Cambridge, and there are lots very close together as the motorway nears an end and attempts to fill some kind of junction quota.
If you decide to carry on, the A604 (I think) into which you end up on is a pretty decent dual carriageway which takes you to the A1 if you want to head up the east coast or all the way to the M1/M6 junction where the A604 acts somewhat like an M6 extension. In this sense, you can probably drive from London to Glasgow, via the M11 without having to change lane once.
May I attempt to throw a little light on the London stretch of the M11? FYI the M11 starts at junction 4 at Redbridge roundabout (where the arrow is on this map). I'm quite sure that the motorway was built in its entirety from London-Cambridge from about 1974-1977 (there are references to ``Cambridge Western Bypass'' from 1974). The reason the numbering starts at J4 (Wanstead) is because it must have been planned to start at Barking. In fact there is now a road running down the Roding Valley, the A406 North Circular (South Woodford-to-Barking Relief Road), which follows the line of the M11 down to the A13 at Barking. It is also continuous with the A406 going arching west to Walthamstow and Tottenham. There are four junctions south of J4, which if it were the M11 could read, going down, J3, J2, J1 and the end/start at the A13. This was built around 1988-89. I remember them building it because I used to live in Wanstead, facing the south of Wanstead Park, just above where the blue 5 is under the arrow on the map above. (In 1991 I moved to Cambridge, exactly the other end of the motorway! I'm sick of travelling the rotten thing.) The road running down here, the A116, used to be the North Circular before they built the new road. All the intersections on the A406 are fully directional apart from where the it meets the Romford Road at Ilford. Due to lack of space, they managed to squeeze in a junction, but I think it is limited.
BTW most of the A406 from J4 up to Arnos Grove was upgraded to sub-motorway standard in the 90s. Also very recently (about 1999) they've completed the A12 route through Wanstead and Leytonstone to connect up with the A102 (formerly the A102(M)). There was a big protest a la Twyford Down and the Newbury Bypass about it in the 90s (check this out). It's a mess. Honestly, when it does happen in your back yard you lose sympathy with the government. But I have little time for road protesters when they are blind to bigger picture either, Twyford being an honourable exception. But London did need it. As far back as I can remember (I'm 24), the upgrading of the A12 was earmarked from around 1980, because all of the houses on the south side of the A12 through Wanstead were obviously under compulsory purchase orders - all boarded up and crumbling. We now have a fully continuous dual carriageway north-south through express route through East London from the M11 right through the Blackwall Tunnel to the A2 Rochester Way at Kidbrooke. But I digress...
As for extending the M11 north, they could upgrade the A14 to motorway standard (all the rest of the A14 is), from Cambridge as far as the A1 at Alconbury, and rename it the M11 (A14), i.e. the A14 follows the M11 then branches off again.
Travelling south from Cambridge, there is about an 18 mile gap between J10 (Duxford) and J8 (Bishops' Stortford/Stansted), with no exit southbound at J9, which I think is just a half-mile short of the second-longest gap between exits after the M26. Junction 9 with the A11 (again, upgraded from an old single-carriageway in the 90s) is known as Stump Cross, although not signposted as such, and is sort of the Scotch Corner of East Anglia (whoopee!)
The A604 is now the A14, of course, but more importantly, to get to the M6, you need to turn left at Spittals Interchange by Huntingdon, cross the A1 using the Brampton Hut roundabout, and use two roundabouts at Catthorpe to access the M6. If you continue up via the A1 to Glasgow you need to exit at Scotch corner (and negotiate 6 roundabouts on the way). However, current road construction plans do mean that this should be possible one day (new Cambridge-Huntingdon dual 3-lane motorway and new A14-M6 flyover at M1 J19), with the removal of all the A1 roundabouts making Tyneside another possibility.Peter C. Langdale writes:
Thought you might like a point of clarification on your section on the M11, (as I've just had the honour of working on the various resurfacing projects on it for the last few years). It was built in its entirety from London to Cambridge with two lanes and hard shoulder (all in concrete). In the 70's it was decided to widen it, but only up to Junction 8, with the addition of an asphalt hard shoulder to give 3 concrete running lanes up to J8. Lane 1 is the original hard shoulder and has suffered enormously since.
Also: there are two ``unofficial'' junctions on the M11 which locals use to break up the huge distances between the official junctions. These are accesses to motorway depots, but access is also available to public roads to leave/join/u-turn the motorway:
Naturally I cannot condone this practice; I am just commenting on my observation of their use.