Just buy it, it's freaking amazing. You're just falling in love with the story itself. I have played Mass Effect in the past before on Console, but just a demo/ small bit.
I must say, I have had some moments where I didn't enjoy the game such as on Mass Effect 1. The controls were terrible on PC. But the story sure compensated for it.

Mass Effect 2, fantastic story. Controls were a big improvement compared to 1. But also importing it from 1 made the job a tad easier.

Mass Effect 3, freaking hell where do I start. Considering it's a follow up story of 2, it's amazing. I have imported my save from 2 as well, and continued to play on it. All of the choices I have made on 2, impacted on 3. Outstanding! But also, I find it kind of unfortunate that I didn't get the "best ending" on 3, due to lack of War assets (was missing some things on Mass Effect 2 apparently) made it kind of an okay ending. Was missing 2k war assets in order to get the proper one.

All in all, fantastic trilogy. Would definitely recommend buying the legendary edition compared to the standalone ones. Simply due the remastered graphics, all of the DLC's and a nice launcher for all 3 games.

Update: Finished my 2nd playthrough with a bit more than 7000 EMS and got the remaining achievements to 100% it. I must say, I enjoyed it even more during my 2nd playthrough than my 1st. The game will always have a special place in my heart and my steam library. I chose the Synthesis ending, for the record. And I must say. I can't wait for some time to pass so I can do my 3rd playthrough. Amazing game!