The problem with the first season was that it was slow, packed with back stories and origins of newly introduced characters. It also didn't help that it was loaded with juvenile crap targeted at a preteen audience that would make any adult cringe such as the baby looking amine style to express every emotion, the theme song that sounds like bad karaoke, and their eternal lust for pizza (much to reminiscent of the 80's TMNT cartoon, yuck). Once you get over the initial shock of it's "over the top" style, you'll begin to appreciate for what is is, "fun". You'll also appreciate what a diverse team they are. You got all your popular high-school arch types; the preppy popular kid (Robin), the ditzy cheerleader (Starfire), the jock (Cyborg), the emo (Raven), and goofy nerd (Beast Boy).
Every season of The Titans has one overlying theme. The focus of the 5th is a war between The Titans and The Brotherhood of Evil. The story begins with flash back of Beast Boy being kicked out of The Doom Patrol after not sacrificing his entire team to stop The Brotherhood of Evil's black-hole generator. I don't believe it's an exaggeration to say The Doom patrol are a bunch of sadists who's motto should be, "Everybody gets left behind". I've never seen a team who was so willing to sacrifice any of their members at the drop of a hat, but it's a good contrast with the Titan's almost childish "Nothing is more important than friends" policy. Don't get me wrong, I value my friends, but protecting the world from the constraint threat of annihilation can sometimes require sacrifice. The story also feature "a battle to end all battles" with all the members of the Titans West, East, and the reserves (including never before seen members such as Jericho) and The Doom Patrol against The Brotherhood of Evil teamed up with every villain that was ever in the T.V. series. I find this to be perfectly fitting end of the series.
It also features a couple of episodes that aren't exclusively about The Brotherhood of Evil story-line. One is the series pilot, "GO", which I don't think should count as "new" episode. That's just a super cheap way of having 14 episodes to complete the season. Also, they finally introduce Kid Flash, a popular Titan that should have been in the show since the beginning, in the episode, "Lightspeed". They end the series with a pretty decent, "good-bye" episode entitled, "Things Change".
If your a fan of comic-book cartoons or The Teen Titans I recommend you give the show a chance. Many of the stories are directly from the comic-book series. It's a show for adults and kids with humor that's childish with a slight hint of savvy sophistication. You can enjoy some of your favorite b-list comic-book characters shown in a fresh and fun way. Also, it might take time, but you'll grow to love their theme song. Come on sing it with me,
When there's trouble you know who to call, Teen Titans
From their tower they can see it all, Teen Titans
When there's evil on the attack
You can rest knowing they got your back
'Cause when the world needs heroes on patrol
Teen Titans, Go!