Pros:
Very effective jungling after Executioner's calling
Very powerful
Heal to full in about 2-4 hits
90% crit
300+ damage

Cons:
Weak until level 6
Somewhat disabled by tanks
NEVER, I repeat, NEVER target someone with Thornmail. Kill them last.
Prone to be nuked by mages. (Only if you are slow with hotkeys, Etc.)

My Tryndamere build consists of getting just about 100% crit and high attack damage plus some lifesteal. This is how a 3v3 build NOT a 5v5 build. To start grab a Brawler's Glove and two Health pots. Get spinning slash first. In the beginning gank if done right you should get first blood and maybe another kill. Next always, reapeat ALWAYS, take top. Now until mid game just farm minions, build items, and kill the enemy top if able.

Hopefully if things are done right you should be about level 8 you should have Executioner's Calling, Berserker's Greaves, and if really well, part of Infinity edge. Now you can start ganking =P. All you need to do is just gank, farm, gank, jungle, gank, farm. Just building your items. If doing quite well, they should surrender by the time you are level 12.

Alrighty, You should be about level 12-14, have Executioner's Calling, Berserker's Greaves, Infinity Edge, and Phantom Dancer. If doing really well and you are higher level skip your second Phantom Dancer and go straight for Bloodthirster. By this time once you get Bloodthirster you should be able to 3v1 and win sometimes with ult if you are lucky. You should be very close if not already unstoppable.