The Baldur's Gate series is the best RPG series I've ever played.

Would recommend it to anyone who wants to play any kind of RPG

I would still put CoH above Starcraft II, I prefer the slower pace of action and the use of cover for infantry it is more my type of game

I know a lot of old games that a very good.

Septtera Core

It's an RPG, the world is made up of flying continents that are situated at different altitudes. The combat is real-time, sort of, each character, you can have three in a battle, has a little circle that fills during the battle, depending how full it is you can use different attacks, there are also some cards you can use that have different abilities from direct damage to healing, and if they are used in combinations you can achieve spectacular results.

It plays faster than shown in the video.

You can buy it from GoG.com for $5.99.

Titan Quest series

They are similar to Diablo in game-play, but they don't have the annoying identify items and you can generate a portal anywhere to get back to a town. They are set in Greek mythology.

You can find on several DD stores, and maybe in physical stores.

The Elder Scrolls series

I've only played Morrowind. They are WRPGs with a big overworld, it could take hundreds of hours to do all the quests and go through every dungeon.

Steam is having a sale today on The Elder Scrolls IV: Oblivion® Game of the Year Edition Deluxe.

SpellForce series

RTS/RPG hybrid series. I will mainly talk about the first game in the series, you play as a Rune warrior which are people who have had their souls sealed in a rune. The main characters can level up, but the up to 5 additional characters you can have are chosen from ones that are at a fixed level and you can swap them out. Most maps are RTS, while some are like dungeons in Diablo.

Several DD stores have them.

Freedom Force series

It is an RPG series, in a way. You have 4 heroes in a mission, you can choose from a high number of pre-made heroes or you can make your own.

Again they can be found cheap on DD stores.

Star Wars: Knights of the Old Republic

I don't think I have to describe this one.

Aquaria

It's a Metroidvania platform under water.

It's on Steam for $20.

I know some others I'll list them later.

Rome: Total War, and its total conversion mod: Europa Barbarorum

http://en.wikipedia.org/wiki/Europa_Barbarorum

Vanilla

EB

HUGE MAP

I know  it's not an rpg but civilization is one of the best pc franchise so I recomand you to get civ V when it comes out.  It's just an amazing franchise

FFXIV when it comes out. 

Depends if you're willing to play games with dated graphics. Some of the best games are older or had small budgets. These are off the top of my head.

RPGs:

Definately check out The Witcher. Otherwise:

Mass Effect 1 & 2, Star Wars: KoToR 1 & 2, Neverwinter Nights (old), Neverwinter Nights 2 (not so old), Baldurs Gate 1 & 2 (very old), Icewind Dale (very old), Planescape Torment (old), Mount & Blade (low budget).

It's also worth checking out Deus Ex (old), which in my opinion is the most rewarding single player game ever created and mixed FPS and RPG genres together.

Also, if you haven't bought them on PS3 yet, it's worth getting Oblivion, Dragon Age: Origins and Fallout 3 as the modding community on those 3 games is amazing.

FPS:

Metro 2033, Half-Life 2 Episodes (check out Source mods too), Left 4 Dead 1 & 2, Stalker series, Counterstrike: Source, Crysis.

RTS:

Starcraft 2 is the obvious one, but also don't forget about the original which is still great. The Total War series is also worth looking at and is fairly unique. I've always been a bigger fan of Age of Empires. Many will tell you 2 was the best but 3 and Age of Mythology are worth a look at too and have decent campaign modes. If you do like Age of Empires then you'd probably also like Rise of Nations. Warcraft III was released before World of Warcraft and is a nice look into the Warcraft universe without having to sign up to the MMO. Finally, Darwinia is a good little indie title.

RPGs:
Star Wars: Knights of the Old Republic 1 & 2
Neverwinter Nights 1 & 2
Baldur's Gate/Icewind Dale/Planescape: Torment series

Adventures:
Grim Fandango
The Longest Journey 1 & 2
Indigo Prophecy
Myst: Masterpiece Edition

Strategy:
Total War series
Civilization series
Warcraft/Starcraft series

Torchlight (dungeon crawler)
Plants vs. Zombies (Tower Defense)
Misadventures of P.B. Winterbottom (Braid-like game)
Trine (Side scroller kinda game)
Machinarium (brilliant point-n-click)
Red Faction Guerilla (Open-world, great destruction physics)
Tropico 3 (city builder)
Sins of a Solar Empire (RTS)
Serious Sam HD: Second Encounter (old school crazyass fps)

and there is nothing wrong with that but I was under the impression that you were looking for new games and considering SC2, would you prefer I recommend Company of Heroes instead? Because that seems kinda redundant.

you may like to try Men of War, Soldiers and Dawn of War 2 they are more real time tactics than RTS but Men of War and soldiers have that slower passed cover based strategy you like.