I'm pretty optimistic. So far I've liked most of what I've heard of, or am neutral on it. I think I'll reserve serious judgement until there is more of real substance to judge, such as a finished class preview or some finalized crunch that directly relates to magic or a class feature. It's most likely that my group will be in the middle or beginning of a year-long run in 3.5 or another closely related game system so it's unlikely I will be an early adopter. It seems very likely that I will pick up the books as they come out unless between now and then there is a revelation that just sours me on the whole thing. That seems very unlikely, but it could happen.
'It won't be D&D!' falls on deaf ears to me. If it means finally kicking a lot of the conventions of the past to the curb, then I'm all for it. D&D has a lot of baggage that it could just as well get rid of and 4E might be a good place to start. 3E got people used to the idea of change, and to my mind 4E should introduce much more change. In some ways, even change for simply change's sake is good. The look and feel of monsters? Change away! Make kobolds into small earth elementals. Make dragons into legless wyrms that burrow into the ground or live in the sea. Give elves tails and dog ears that stick out at 90-degrees. All those are minor, little cosmetic changes.
'4E will be a new game!' is a heartening cry to me. It holds out the hope for real, lasting and substantive change from the past. I don't think that 4E will be as radical a change as a lot of people seem to think; certainly not nearly as radical as I would make it.
Radical change means a lot of different things to different people. To one person, 'radical change' might mean 'we cut out monks and assassins and half-orcs'. Pah, those are cosmetic changes at best. The makeup and number and distribution of classes is a cosmetic change. Combining Arcane and Divine magic is a moderate change. Getting rid of (and keeping rid of) certain spells, such as Teleport or Detect Evil, is a moderate change. Radical change to me would be 'We now have three stats: Mind, Body, Soul' or 'Armor takes off from damage' or 'There are just three broad archetypical classes and all changes are made with feats and talent trees'. 'There are no more hitpoints, just conditions you acquire'. And I'd probably go further than that.