Infiltrator was the first class with which I finished trilogy. In the first game, she was a nice mix of combat and tech, but in the end, most of it came to shooting things with sniper rifles, while firing an occasional hack. In the second game, she became even more boring, since it was just TC ---> headshot. Fire an occasional incinerate and hack, but that was it. Third game didn't saw many changes to her.
Final verdict: an effective class, but rather boring one. She is saved from being worst by her tech abilities, but in the end, nothing to write home about.
Vanguard was the second class. In the first game, she had a nice mix of defensive and offensive abilities, combined with good crowd control. She was very good at killing things while getting in their faces, but also had the capability to stay alive while doing so. She was a great class in the first game. Come second game and the addition of charge and I feel in love with her. Suddenly, she was all about offensive and screw the defense, but there was more to her than just charging. You had to read the battlefield, choose your target and watch for the other enemies, so you didn't get overwhelmed. She became a chessmaster, playing the battlefield and the enemies to her advantage. Vanguard was at her absolute best in the second game. Third game saw the inclusion of nova and while it was great as far as fun went(I mean seriously, you literally became a human bomb), the element of planning was gone. Now you charged, novaed, repeated. Vanguard gained a lot of fun by nova, but lost a lot of allure by it.
Final verdict: very fun and effective class and, despite what I said, my second favourite, all things considered.
Engineer was the third class with which I undertook the trilogy. And despite what many say, I never found her particularly weak in any aspect. Sure, her powers aren't as good as those of adept or vanguard, but she can effectively negate enemies, turn all but the toughest synthetics into allies and in general, she was very fun to play. In the second game, the fun continued, as she gained a little helper in the form of the drone. Overload and incinerate took care of most defenses and while AI hacking and cryo field were useless due to playing Insanity, the game was still fun. If I could use those two abilities as well, it would be even better. In the third game, the engineer really shined for me. Even on Insanity, all of her abilities were once again useful and I felt a little like elemental wizard, with all the bursts of electricity, fire and ice coming from me. Sabotage was great talent and I could finally screw with enemies again, disabling their guns, turning enemies into friends and in general playing havoc on battlefield. It was really great. The addition of turret and more drone goodness were really nice to me. Also, seeing Liara is always my LI, I just loved the idea of a biotic and tech specialist together, complimenting each other.
Final verdict: an extremely powerful class, able to deal with just about anything and easily my favourite. I consider her my canon.
Adept came up fourth. No surprise there, she was extremely powerful in the first game, being able to lock down the battlefield in manner of seconds. I adore battlefield control, so I had great fun with her. In the second game, playing Insanity, she was a little lackluster, due to prevalence of defenses that effectively make an adept all but useless. She was saved from that fate by me taking stasis as bonus power. Would I play Veteran on lower, she would be a beast. Come third game, she was back to her old power with biotic explosion and everything.
Final verdict: a class tailored to my playstyle, but in the end, she rates just a little bellow vanguard, but much higher than infiltrator.
Soldier was my latest class. And frankly, while she was effective as all hell(seriously, I think this playthrough saw the least deaths of them all), she was also boring as all hell as well. With her, it was shoot, immunity, shoot some more in the first game. Second game was a little better,with AR giving you that Matrix feel, but in the end, it was still about guns and ammo powers. And the third game... more shooting, with AR loosing it's allure to me and CS(which was totally ignored in the second game) taking the forte in it's stead for a lot of fire explosions. Easily the most boring playthrough.
Final verdict: an extremely effective and powerful class, no matter which game, but also easily the most boring and least exciting one.
Haven't played sentinel yet.