Things I liked: The PCR-97 M4 by ICS has a very soild, heavy feel to it. It is a great CQC weapon and definatly gives you more bang for your buck. It is easily upgradeable and with a little know-how is one of the best weapons for a do-it-yourself mod.
Things I would have changed: As nice as the PCR-97 is it is easy to break it if you don't upgrade it right. After a while pieces may loosen and get lost. Scres to replace old ones are very hard to find.
What others should know: The M4 is a great choise if you want to move up from lower powered guns to AEG's