So i want next month or so to buy an 21.5" imac (2.9Ghz, fusion drive,650m geforce). I think i will keep this at least 3-4 years.So i read all over the place, only here on this forum at least a dozen of people who complain about this new machine, and attention in the manufacturing of apple products began early with the iphone 5. My question is...this issues will be there still after 1-2 months ?
First off, you're being way too vague about the issues people are having with the 21.5" iMac. Secondly, going from a desktop PC, you are making a few sacrifices such as lack of easily upgradable/replaceable storage. On the 21.5" iMac you need to pre-configure it with 16GB of RAM or you're stuck with 8GB unless you go through the arduous task yourself of upgrading it. You're also stuck with the GeForce GT 650M (or 640M if you decide to go with the lower-end model). If you are fine with that, then it is a decent enough machine.
The only issues that I've been reading about with regards to the new iMacs are with the 27" models. The 21.5" models, from what I can tell, seem to be more solid than any 21.5" iMacs that have come before it. I don't think you will complain about it and I think you will be happy. Though, given that it is an iMac, buy AppleCare as that'll cover you for three out of your three to four year period of owning the machine.
The only thing that might annoy you (and was the thing that has forever deterred me from getting an iMac in the future) is that it is, by far, the hardest Mac to upgrade the storage on. 1TB will be nice for today; you might want more tomorrow, and that's harder to rectify on the iMac than any other Mac. If that doesn't bother you or if you aren't worried about it, I say go for it.