If you don't have a constant internet connection every time you want to play...well you're in for some disappointment. The game's appeal focuses mainly on its massive and competitive multiplayer community, the single player mode is just extremely limited. Oh and don't try to out-muscle (out-macro) an insane AI. At least not if you're not really really good.
The community is far better than Call of Duty's, partly because it's for PC users (which boasts a more mature fanbase, unsurprisingly) but still in some regards hostile. People with extremely sensitive feelings should steer away from multiplayer and multiplayer chat. If you aren't an instant starcraft genius the trek up the ranking ladder will be arduous and you will be frequently called "noob" (a term which means new player) and often it will have derogatory connotations to it. Don't get me wrong; noob isn't intended to be insulting, but a lot of people will use it as so. Some examples of which consist of "man you f--- noob i'm not playing with you no more". At the end of games it's customary to say gg (which means good game) but particularly troll'ish players, especially those who feel like they've been cheesed or hustled, will feed you a variant like "gg B--". I am occasionally guilty of it myself.
Oh and prepare to lose. A lot. And by a lot I mean on average about 50% of your games. Some of them simply won't feel fair.
If you get past the competitive metagame which is actually a professional sport, you can try out the custom games (they've done some spectacular things with starcraft). Don't believe me? Think I'm exaggerating? There have been first person shooter mods, albeit not very good, based on starcraft. There are DotA ripoffs and Diablo clones, rpgs, Civ clones, tower defense, counterstrike starcraft edition, etc. etc. My personal favorite doesn't deviate away from the starcraft metagame too much; it's team monobattles. You work on a team of 4 against another team of 4 and each member is restricted to only building an army consisting of one type of military unit. The problem being that many units are hard counters to others so you need to communicate and coordinate with your teammates. It builds character.
As for positive role models...well...I can think of Matt Horner, and to a lesser extent Valerian Mengsk, who is using his power for "good" in that he's purifying Char, the zerg homeworld. Otherwise, the protagonist who's supposed to be Jim Raynor...is an alcoholic mess of an individual who in my opinion was simply a massive jackhole many a time.
And hey, regarding the violence, the protoss deaths are the least violent. However, if you do have models turned on to a high setting (basically default graphics medium or above, for the less graphically literate), terran biological unit deaths are rather violent. For example, if fried by laser or flame type weaponry biological units will flail in agony before collapsing in a charred mess. If attacked by explosives they will...well, basically fall apart. If attacked by blade-like weaponry marines and marauders can be cut in half for examples. ALL zerg units...almost NO exceptions, die very gruesome...and frankly unrealistic...deaths, for example the ultralisk splits apart and you can see all of its internal organs. When zerg buildings "die" they leave behind a gory mess. The violence part of the game makes a lot of M-rated games feel lightweight, but hey I ain't complaining.