Mass Effect 2 is the second game in the series, the second best game in the series, and the second worst game in the series.
Its where the series hits its graphical and aesthetic peak IMO. 3 was... off. Very off. Some places looked fine, but faces looked terrible at times, animations were often awkward, and the aesthetic was an odd mix of both 1 and 2s where everything was clean but dirty. It was weird. Not bad, but I didn't like it.
2 on the other hand, looks great. The aesthetic is consistent, and almost everywhere looks pleasant. The lighting works well, and there aren't a lot of weird animations of facial features.
I personally disliked its combat, and its vehicle sections. The combat was boring and bland. It consists of sitting behind a wall, waiting for either the enemies to stop shooting or your health to regenerate, so you can look over the wall, shoot for 3 seconds, then hide behind the wall again. I prefered 1s over it, with different missions requiring different tactics [Some you would have to stay in cover, or get swarmed by 1 hit kill rockets or snipers, and others you could just run and gun through], as well as its inclusion of ranges greater than 10 metres, so I could snipe my enemies from 500m away if I so chose. 3 was good in combat too. You moved around more, enemy types were different so you weren't just facing the exact same enemy the whole game through [Fine, 3 types of enemies. Ones with just health, ones with health and armour/shields/barriers, and ones with health and armour and shields/barriers], and the weapon dynamic was more fun than in 2, where you were locked to only using your 'class weapon' types, whereas in 1 and 3 you could use any weapon, just your effectiveness would suffer somewhat for it [In 1 not all classes could train in every weapon, so an adept using an assault rifle would have reduced accuracy and such with it, whilst a soldier fully trained would be fine. In 3 heavier weapons meant longer cooldowns on abilities, so classes dependent on their abilities like the Adept could either carry 1 heavy gun like a sniper or assault rifle, or a couple of smaller guns, like pistols and SMGs, or have a +150% penalty to ability cooldown times].
Hacking and bypass minigames were the best in the series. 1's was... Meh, and 3's was non-existent.
Vehicle... Hope you like flying a tank made of tissue paper. No, really, this thing takes like 10 shots from a pistol and blows up. Slight exaggeration sure, but that's about it. Made gameplay in the Hammerhead terrible. The Mako was good. Some found it hard to control, IMO it was actually pretty easy, it had a lot of health and shields, a big gun and a machine gun, but it was still very vulnerable if you didn't take care of it. It meant you could go into a firefight and sit around shooting for a while, or driving in circles and gunning, whereas in ME2 you'd have to find a hill or cliff, shoot 3 times with your rapid fire low damage rocket launcher, then hide behind the cliff for fear of blowing up.
The story... Meh. It was alright. It did nothing in the slightest to advance the main plot of the series until the final 30 seconds, but it wasn't offensive and was generally enjoyable to playthrough.
Tips? Play Vanguard. No, seriously. In 1 the soldier was OP due to health regeneration. In 2 and 3 the Vanguard is OP due to charge.
If you're not playing the Vanguard there's only one tip that really matters; don't be an idiot, and don't get bored. The only way you can die in this game is if you leave your cover to fight an enemy either because you think you can take him and his 3 mates full clips of ammo [Hint, you can't, you have no health in ME2 for some reason], or you get bored of sitting in cover and decide to just screw it and pop up to shoot someone. Do that, and you'll die. Don't do that, and you literally cannot fail.
Oh, and note what each crew member is good at. You'll need to know at the end of the game. Or you could lookup a walkthrough, but that's no fun.