My reactions to various details over the course of these several months has been very hit-or-miss. I'm excited to actually get my hands on some mechanics so that I can judge for myself. Lately I've liked what I've heard, so I'm really optimistic about this.
Oddly, one thing I'm looking forward to is the simple, bare-bones "core" that lies at the center of 5E's modular design. Several weeks ago I got a request for a quick game with a mix of new and very inexperienced players, and I just didn't have the energy (or inclination) to work up some pre-gens and design something with 4E, not to mention that I didn't have my battlemat, markers, minis, tokens, condition tracking paperclips, and power cards with me. I would have run The One Ring (since it's a simpler game with faster character generation), but it caters to a very specific tone and setting (obviously, being set in Middle Earth) and that wasn't quite what I would have gone for. To sum it up, I never ran the game and wished I had a really simple system that would have made it easier.
I've looked at some 1st and 2nd edition stuff, as well as D20 Microlight and some of the retro-clones, and they all have some combination of out-dated, clunky mechanics, rules that I'm not familiar with, and balance issues, among other things. Looking at it from this angle, it would be phenomenal if I could run a simplified game for a new group with the same rules (familiarity is key when GMing) that I use for my regularly gaming groups minus any tactical/complex modules. I think that's when the major strength of having a single, modular system really hit me.
In any case, I'm sure I'll have more to post come tomorrow (depending on what type of agreement WotC makes you sign before accessing the playtest materials).