Well, it's a completely different game from Descent - in my opinion. First of all, it's much faster to set up and play . After sorting all the cards and tokens (plastic bags, separate boxes etc) it now takes us about 10 minutes to start playing. But these are small (but important!) things.
This games plays a bit more like Arkham Horror than Descent. For me the big difference is, that after a few games of AH I was a bit bored - yes, the game was good, but usually one player took over, commanding the others etc. It could be played the same solo, but with many characters. Games like Battlestar or MEQ change this - you play against a living opponent, and every game is different.
MEQ gets better after a few games - when both Sauron and Heroes know the rules, can start to anticipate each other rules, guess and second guess the missions etc. We were really in two minds about buying this game (it's not cheap!) but now we're so happy! We've been playing for the last 2 weeks, every other day or so, and this hadn't happened before with any other game we bought.
What can I say more - I think combat in Descent is very important. MEQ is more like hm..chess, where combat is fast, fantastically executed, but just an element of the game. Far more important is aticipation of your opponent's moves - though luck is also a major factor!
Hope my rambling helped you a bit, and now back to work for me... But I want to sleep too..