Finally, and after almost 33 hours of gameplay, I've finished my first run of Mass Effect.
At the end, I've done almost all sidequests (excepting two of collecting data), explored (I think) all the galaxies and planets (you can see a list of what I've explored here), and this were my stats:
Gel: 999 (max)
Money: nearly 1.5 million
Level: 47
Class: Soldier
Alignment: Paragon (Good)
Specialization: Shock Trooper
I acomplished the romance sub-plot (with the Asari girl) and completed tons of encycloapedia entries.
Now that a Hardcore difficult level, level cap of 60 (instead of 50) and more important, the option to start a new game with the inventory and experience of the previous game, I'll probably do a second run, this time being a renegade (Bad) character, and trying to get to level 60.
Overall, it is like playing "KOTOR 3" but without jedis. The engine has some flaws, some parts of the game seem a bit unpolished, but anyway it is one of the best 360 games in the market, has some cool replay value, the graphics are fantastic and it's an RPG :)
Time to go for The Witcher too at last!
P.S.: A guide I've found that contains all the missions and submissions can be found here at GameSpot. Is not complete but you can do every primary and secondary mission.