Yes, some of them are amazing, some of them are just good. None of them are really dogs (at least that I have used). The best (technically) tend to be the newest versions, particularly the 15mm and 19mm elmarits, new zooms (21-35, 28-90, 35-70/2.8, 70-180/2.8), the 28/2.8 (latest), 35mm f/1.4, 50mm f/1.4 E60, the 80/1.4 (for its look more than its MTF) and then the APO lenses like the 90/2 APO, 100/2.8 APO, 180/2.8 APO, 180/2 APO and 280/4 APO as well as the uber-expensive APO telyt-system.
All the lenses listed above are superb, with many photographers preferring them to L lenses. Some in particular are unquestionably superior to the Canon equivalents (15 and 19mm, 100/2.8 APO, 180/2.8 APO, 280/4 etc).
The 2 cam 3 cam thing is best answered at Andrew Nemeth's Leica FAQ:
http://leica.nemeng.com/001c.shtml
Suffice to say that 2 cam is older than 3 cam is older than ROM. Since you are not using it on an R, it does not matter much other than with respect to age. Most of the newest lenses are only offered in 3 cam and ROM.