It depends what you're looking for.
The first one has a good story, heavy on the RPG elements (some of them detrimental imo, I hated going through hundreds of identical weapons in my inventory and the levelling system is a bit meh) but horrible shooting/fighting mechanics and the mako sections were just atrocious. Oh yeah... the elevators... Overall, I thought the game was pretty average but a good introduction to the Mass Effect universe. It had an identity crisis where the devs wanted an RPG with shooting but had no idea how to create decent shooter mechanics.
The second game massively improves the shooting mechanics to the point where it can stand up as a competent shooter. It's refined in that the Mako sections are completely removed but also some of the RPG elements are reduced (levelling is much simpler, fewer weapons). Story-wise it focuses heavily on the characters and you learn a lot about the universe of Mass Effect by doing the well-thought out character missions. The characters really come alive in this one imo.
ME3 is a good title on its own. It further improves the shooting whilst bringing back more RPG elements. It only has one true hub area but that's in keeping with the general story of the game. It's pretty heavy on story and is actually quite dark and depressing in tone. The ending is not great but it's not anywhere near as bad as the internet would have you believe, especially with the free DLC. The multiplayer is actually quite fun too; playing a Krogan Vanguard is quite hilarious.








