I used to be relaly into it (hence the username), but they kept dumbing it down and I got fed up and quit.
One thing to remember, they keep bringing out updates, but not evenly for all. For example, the dark eldar recently got some new stuff, for the first time in 10 years or so. Meanwhile, marines have been updated and revised 3 times for the main groups in that time, with all sorts of new ones added and updated as well. Dark eldar players were really left in the lurch. Squats for 40k and Chaos Dwarfs for WH were quietly removed from the universe. Loads of old Imperial Guard models can still be used, but they aren't sold everywhere anymore, if they are still being made...if that was your army, tough. If the army you choose doesn't sell well, you're sorta stuffed.
On the other hand, not being updated be a good thing. The backstory and setting changes more than in your average comic series. They like taking armies and changing the theme when they update them. The Flesh Tearers used to be particularly nasty and aggressive, then were having problems with too many members going insane and now have realised they'll be extinct soon, and have decided to go out in a blaze of glory. The Dark Angels used to be warrior-monks, but now they are all traitors committed terrible crimes to cover up their terrible crimes. If GW decides to change the theme of your army in a way you don't like, you're stuffed.
This also applies to individual units...you might have lovingly painted your expensive models, only to find that there wasn't room in the rulebook for them. Up til recently, a number of tanks weren't in the Imperial Guard book anymore, despite them existing in previous issues and models being sold. Or they way they work has changed, your army built around a certain thing isn't viable anymore.
