Pour said:
Apologies if this is a newbie question, just trying to expand my horizons of the roleplaying game genre.
Pour, this is an excellent question.
I highly recommend expanding your gaming horizons beyond D&D. Not because D&D is bad in any way, but the RPG world is much wider than most gamers know. Also, I suggest not just looking at new games or currently sold games, but checking out out of print games that can be found cheap on eBay.
Making any kind of recommendations is tough not knowing what you like to play. Finding players can be a challenge sometimes, but I find that most groups are pretty flexible about trying out a new game for a one-shot or a short campaign. When introducing a new game to friends, don't say that this is the D&D replacement for the next decade. Introduce it as something fun to try for an evening or a few weeks.
The game I always suggest new players try out is Call of Cthulhu. CoC is extremely different from D&D and incredible fun. Outside of D&D, CoC is the most popular game run at conventions in the US. It's about investigating strange horror in the 1920s and great spooky fun when run correctly. CoC is not about becoming powerful, or even surviving, but saving the world from That Which Should Not Be.
If you are looking for just another fantasy RPG, then I agree with the Warhammer suggestions. It is an powerful setting for great stories and combat is wonderfully brutal. If you enjoy low-level D&D, then you might like Warhammer. However, if you much prefer high level D&D play, then you need to check out White Wolf's Exalted RPG which is anime fantasy with an exciting setting and huge company support. Personally, I prefer Exalted 1e.
BTW, if your group likes spellcasters, hunt down an RPG from Key20 Publishing called Eldritch Ass Kicking: the Game of Old Men with Sticks. It is a humorous RPG where everyone plays a crazy wizard and you create spells, counterspells and golems on the fly to battle each other and the various villains across the setting. Every time I have run this game at conventions, 3.5 players get really excited because of the freedom of play.