Congratulations on finishing CSB! It definitely has some of the greatest level design ever made, and there is so much in it that you can still learn new things if you revisit it countless times - I found something new on my 10th game!
I never really liked DM2, there are some nice parts, but overall it didn't really "feel" like DM. I'd prefer a custom if I were you. My personal favourite so far is Towers of Chaos by PaulH. The recent Surgical Strike by Sophia seems to be very good as well, but I haven't played it yet, so I can't comment on that one; many people seem to like it very much, though.
Of course, there is always the infamous Conflux II by Zyx, but beware that this dungeon is VERY hard. Furthermore, Conflux III is currently in the making, so I'd wait until that is ready before you play it (and I guarantee you that Conflux III will be vastly superior to Conflux II).
Other great dungeons are Imprisoned Again by Sucinum and The Black Flame by PaulH, though I prefer Paul's Towers of Chaos.
Hope this helps, and have fun playing more DM.
