what are the bad points about Warriors?

Warriors are immensely gear dependent - because you have no real ways to avoid damage, you cannot compensate for weaker gear in the way that Hunters, Warlocks, Rogues or Mages can by simply not getting hit. Especially in solo play, once you've started combat you're essentially 'locked in' for the duration with a very limited number of escape tricks if the combat turns against you. There are a wide variety of tricks you can use to enhance your survivability, but if you're running around in outdated greens you ARE going to take a beating every fight.

Warriors are very dependent upon support classes for PvP. While you certainly can have some success as a solo PvP warrior, in most cases you will find yourself crowd-controlled in some fashion and completely unable to produce any real damage. As a corollary to that, though, if you have good support (a Paladin in particular is absolutely wonderful to pair with a Warrior) you can smash faces in.

And, finally... tanking isn't easy. You have to deal with bad healers, DPS classes that will ALWAYS pick three different targets - none of them yours - and complain when you can't keep the entire pack on you. Moreover, as the tank you will traditionally take command of the group, which is both a blessing and a curse depending upon your point of view. You won't have to deal with a real moron leading the group (unless... you're the moron, but given that you're reading my guide I'll be charitable!) but you do have the job of whipping the idiot pickups into shape every instance run. On the other hand, at least you'll know that the tanking job will be done well... find a good healer buddy if nothing else - DPS is replaceable, and fairly easily trained - and you'll do fine.