To save people time if they've ever considered looking into a new anime, I'm going to micro-review each one I've seen. Here's the system:

5 - Really, watch this.
4 - Time well spent once you've exhausted the 5s.
3 - It's this, or homework.
2 - Even I can't cope with these.
1 - The mere mention of the title should make you shiver.

===5===
Seto No Hanayome : So funny that I truly have to ensure a good oxygen supply to the room before watching an episode.
Full Metal Panic : They get the balance right between high school romance and mech combat by the third season. Insane animation throughout.
Death Note : Freaking flawless. Until season two. So damn good! Until season two.
K-On! : Just makes you feel happy. Come on, this is deviantART.
Kanon : Really gets to you. For God's sake, watch the 2006 edition, though.
Touhou Anime Project : Very unique colouring. Only one episode so far, but I want more badly.

===4===
Lucky Star : Novel at first, but gets tiring.
Toaru Majutsu No Index : Science versus religion.
The Melancholy of Haruhi Suzumiya : Tedious at times, funny at others.
FLCL : Either dub was fine. Still batshit crazy, though.
Elfen Lied : Can't remember much about it, but it was good drama. Very gory.
Dragonball Z : Gets worse each saga. But, really good memories of this for revolutionary fight scenes - English dub recommended.
Zero No Tsukaima : Often funny. Can't recall much.
Ouran Host Club : Bring your security in masculinity with you. This is often great fun.
Vampire Knight : I recall this being interesting at first, but it eventually got too depressing for me. Nothing happy occurs, ever.
Rozen Maiden : Can't really remember, but nothing really repelled me.
Clannad : As good as a drama + comedy mix gets, but penalised for Nagisa.
Gundam Wing : All the politics is way too confusing, but the characters and fight scenes are intense. Watch the English dub for once. Oh, and the music is incredible.
Yu-Gi-Oh! : Such a cheap anime. But so addictive. Cards! Monsters! Hair!
Bleach : Really exciting at first, but they ran out of money and passion as season 3 ended.
Minami-ke : Sometimes good, sometimes not. Just enter without expectations.
Naruto : First 80 or so episodes are quality, but then filler strikes. Famously.

===3===
Shakugan No Shana : With a better director, this could have been gold.
Mai HiMe : Could be a lot better. But it's not.
Welcome To The NHK : Interesting concept, well-presented. Plot could have been a bit more daring, though.
Negima : Can't remember. Still, see below.
Love Hina : Waaay not-safe-for-family. Standard Ken Akamatsu fare.
Sola : Very interesting, atypical finale. Can be too sterile at times.
Air : You're obliged to watch this if you're into Kyoto Animation, but it's nothing amazing.
Haibane Renmei : Feels like watching a really long Ghibli production. Not much happens.
Cardcaptors : One of the first animes I ever saw. Can't remember much about it.
Toradora! : Inconsistently good - read the manga instead.
Jigoku Shoujo : Watch one episode, and you will have watched them all. You'll see what I mean... So leave it at that.
Black Cat : Good characters, awful directing. Had such potential.

===2===
Shugo Chara : The only appeal of the manga was the artwork, and the anime has lost even that.
School Days : Lame lead role is lame.
Hayate No Gotoku : Why do people like this so much..?
Tokimeki Memorial : Proof that I'll watch anything when I'm ill.
Katekyoushi Hitman Reborn : Really doesn't have anything going for it.
Kannagi : Has such potential, but is butchered by the director who got fired early on from Lucky Star.

===1===
The Tower of Druaga : Crunchyroll, why do you give a crap?
Battle Programmer Shirase : Ahahahah. Apparently they apologise to the viewers in the last episode. The 'viewers' are written as including people pirating subtitled episodes of the series. Genii.

I've watched a few others, but these are the only ones I've watched enough episodes in to form a valid opinion. Look how much time you're saving!