I'm lvl 35 inf shadow and a regular forum reader to see what folks are discovering about our class and i dreaded Tatooine and than Alderaan since many posters had difficulties with those two. Reading the forums i dread hitting mid 40s, since there are shadows (except tank spec) that ragequitting not beeing able to coupe the solo content, in my guild also... since i follow the forums for some time i don't think there is much of a difference between our light/dark mirror's.
Personally, I have all the orange stuff you can get (me and my annoying healing buddy also) modded with blue up to my lvl mods (im cybertech so i actually make and store them in the bank well before the level req), on the planet i mostly don't need to take qst reward in items only in poins since my gear is better, so i get enought points to update my lightsabre and enchantements early on, also I land on a planet usually a level above the said req and i had no problems whatsoever till my level soloing normal content/some 2+'s (including elite - gold mobs, in some sideqsts i think i died 2 or 3 times to an elite but not in the main storyline, i read on viv before the encounter tho ).
I hope it all comes to (as it did untill now) strategy and use of you abilities and companions. I was more of a spank1/spank2/spank1/spank3/finishing move player, but in SWTOR I had to adjust my playstyle lvling up, from using 2-3 abilities on regular basis to using 6-7, learning to cc, interrupt, which abilities to interrupt, use my companions with thought and i love it. It's not as some old school RPG/MMORPG stuff i started with decade or more (lol) ago but a bit "harder" than some other popular "hold my hand" leveling MMOs. I don't have the time to play more than an hour or two a day, so it doesn't bother me not beeing among the best geared, highest level, first to finish folks.
Untill my level i enjoyed the class and i hope with adjustements i will coupe with the content till 50. I can't comment on dmg of inf shadows in the endgame, as i hear we are not the best, but so was said for the class i played in the other mmo and i was ussually among the top dps...