Anachronox?

If you are really into Sci-Fi and especially space operas, there is no way around the Mass Effect series. That is one long declaration of love to the Sci-Fi of the last century. It borders in some elements more on "hard Sci-Fi" but it pulls it off very nicely. The amount of references they pull of is mind-numbing. And I personally consider their description of space combat the most realistically in fiction I've read so far. (And you only read it, because it isn't depicted in the game itself. As space combat is boring, they had to make some "story adjustments" to make it look a bit more interesting).

The background "glossary" easily has more text than many other RPGs have in their whole game and is interesting to read by itself.

Sundog is said to be excellent, but I haven't re-tried the to make the required atari emulator work yet.

All Elite-likes are RPg-ish, things like Freelancer, the X series, etc. You just control a ship more than a character. I've heard Space Rangers is more polyvalent.

Although linear and a bit consoley, Kotor and Mass Effect have good space opera vibes, and sometimes make you believe you're in control of something.

Also, I couldn't get into Albion, but many consider it a brilliant RPG.

Albion is definitely a good choice, but it's impossible to get a copy of it nowadays. Mass Effect is great. You could also try the Star Wolves series, which are pretty good. Just avoid Star Wolves 2 because it's a buggy mess.

Chronicles of Riddick Assault on Dark Athena, this title also includes remastered Escape from Butcher Bay

RAGE by id is a good one also albeit a bit linear

Borderlands and the upcoming Borderlands 2. First one is a great game with so many hours playability, one of the few titles I actually purchased DLC for - Zombie Island of Dr Ned is just like Scooby Doo!

Rogue Trooper & Judge Dredd - Dredd Vs Death if you like the 2000AD comics. Good titles that fit nicely with the worlds created by the artists.

Red Faction Guerilla & Armageddon. Set on Mars, Guerilla is more like Total Recall so not to many aliens on it but the red planet setting is good. Armageddon is also set on Mars but a lot of it is under the surface in caverns and outposts. Still a good blast though.

AvP 2010 version (Even the 2000 version and AvP 2). You get 3 scenarios on each game for Marine, Predator & Alien races. Damned fine shooters all of them. On AvP 2 when the Predator is hunting you it does strike fear for your safety as you get glimpses of it and what it is doing. Good stuff.

Knights of the Old Republic 1&2 - Enough said really with these titles, Star Wars fans love them, RPG fans love them. Huge games with decent stories and still look pretty good considering their age now.

Giants Citizen Kabuto, hilarious game to say the least. Definately Sci Fi with so many different characters, 3 different sections where you play as different characters in each. Each section is virtually a full game in its own right. Its quite cartooney but captures the feel and humour perfectly.

Lost Planet 1&2 - Personally think the first game in the series is better as the second one is similar to arenas and setup with Co Op play in mind. First one though takes you through a proper story and has a decent mechanic where you have to kill the Aliens to absorb their heat to stay alive on a frozen world.

Unreal 1&2 - Classic shooters set on an Alien world, look a bit dated by todays standards but still solid shooters. Personally feel the first game is the better of the 2 as you are on a planet and are an escaped convict from a crashed prison ship. Second one you are more a mercenary / military type guy, good blast but the setting on the first game was better.

These games I have listed are available on Gamersgate, GOG & Steam. Some I have listed are Steamworks so you will need a Steam account to be able to register and play them. RF Armageddon & Lost Planet are the main ones in that list as the other titles you can get from GG and GOG (If you want Riddick definately get it from here)

Thats just a few that come to mind, theres loads more and I could go on all day!

Except for Chronicles of Riddick (because I haven't played it) I can say that this is a very thorough list.

And I want to add that AvP 2 is the best AvP game ever made. Ignore the expansion however.

I know the OP asked for RPG's but couldn't help do a mixed list, there are some great proper SCI FI games out there. Equally if not more Fantasy which also kind of sits in SCI FI but its not the same.

The bit on AvP 2 when you close the shutter and you see the blast from the Predators shoulder canon is a memorable moment. Then you have to work you way through the huge open topped cargo bays. Took me ages to get through that bit as every time I moved I was trying to dash to the crates for cover wondering where the next shot was coming from. It literally was a game of cat & mouse.

Thanks for the comment SimonG :)

Thanks for your suggestions guys. I have played Mass Effect and I love it. I have X3 and Space Rangers so I don't really need spaceship based RPGs.

Can anyone recommend a Sci-Fi RPG similar in playstyle to Baldur Gate (similar to SW KOTOR)? Anything on GoG?

This is quite good scifi RPG - Planet Alcatraz, but it is olschool, hardcore and russian.

I personally think that rebellion's first AvP is the only good one. AvP2 and the recent AvP are too cartoony for the Alien setting.

But they are very far from being RPGs.

Adventure games could be closer, if you want to try the star trek point and cluck (Judgement rites, 25th anniversary, etc).

there was also oldies like B.A T. and Chaos in andromeda (that was on the Amiga), or even Battletech: the crescent hawk's inception, available on PC.

And FTL should come soon... I haven't played it, but indeed Anachronox is very much praised on GOG. And I'll probably buy it sone day. I would, if I was looking for the ame sort of game as you right now...

KOTOR 1-2 and DXHR!

Salvation Prophecy looks like a very good RPG-lite that is also a hybrid of other genres.

Then there's Incognito which I bought a long time ago, but didn't have the chance to try out.

Have you tried http://www.gog.com/en/gamecard/septerra_core_legacy_of_the_creator ?

How about FTL? It might be bit more roguelike than pure RPG, but it has lot of RPG elements. And spaceships.