I actually started with WH Fantasy back in like 95, EVERYONE in the neighborhood played it and I collected a rather large sized army of Bretonians. Eventually it kinda fazed out and it wasnt untill around 2000 that I statred dabbling with WH40k. It was pretty sweet but it was very time consuming and very expensive. I played it on and off for a few years but I could never decide on what army to collect. I started out with Dark Angles, which was pretty short lived, I never had very many. Later I tried Tau and aquired a decent sized army but grew bored with them. Finally I started collecting Necrons, which were pretty cool. I found them to be a little overly dark and gothic though (yes, I realize that this is the theme behind all of WH40k). Eventually, because of college and the cost and time required to play, I stopped, but it was fun while it lasted.
im have kinda mixed feelings on the new 'nids. mainly cos i only just finished my army with the old models. now they bring out new ones and i may have to rethink my strategies. plus i need to buy another codex. but i guess the new models do look kinda cool. never did like the last carnifex.
I play fantasy and 40K, but I prefer 40K. It's less rigid when it comes to the rules for movement and all that. I got tired of units being right next to mine, but unable to be seen... I have about 2,000 pts of Tau, and about the same number of points for Beastmen (fantasy). I haven't played either in a long while, though, since no one I know at school plays much.
WH40K is pretty sweet although im stuck in the old days (I think 2 editions ago?) with my orks :D personally i think GW has better games on the smaller scale for example Warhammer Quest, GorkaMorka and Blood Bowl; but thats just my opinion