it's a decent lens at a decent price, I don't know of a better one for the range and price and i haven't had a problem with sharpness, in fact some of my photos have been really sharp so it may depend on the copy
but the is and mother board went ( and i didn't do anything, i'm careful with my lenses) in about 6 months...they fixed it for free( warranty) but whose to say it's not going to go out in another 7 months..
i think from now on i'm steering clear from the is. it's working fine now, still don't really care for the 135 end aperture..it's supposed to be 5.6 but seems slower to me..like I posted not to long ago i haven't been able to use it
outside a few times during the day(??)it just won't take the photo, nothing, you can't press the shutter and i don't know if that had anything to do with the stuff they fixed or not. i haven't really used it since just to make sure it seemed to work. however i have also had problems with sigma so i don't know it is any worse than that. i'd probably go with the canon over sigma as at least it doesn't focus hunt every photo i take although some say if you hand pick you sigma copy you can get a good one.
i wish i had gotten the 70-200 f4 and something in a wider angle( not sure which) i
love my phoenix 100mm macro( i know, i know the name stinks and it looks like a toy but i
love the lens so it was the best $140 i've spent, more for just all around use than the macro side. the last few photos i 've posted have been with that lens while my other one was getting fixed and now i don't know if i want to go back to the canon

), the canon 50mm f1.8 is nice also( maybe i just
like lenses that look like toys) so maybe i'd get those 2 and something wider than 50 and forget the wider end of the walk around until i had enough for the 24-70 f2.8 l... like in the yr 2200.
i'm editing this cause i just realized something...i have never had a problem using a cp on the 28-135( which you'd think if it was the aperture you would). chances are you won't be using a cp much in dark conditions anyway( so at 5.6) and the problems i
did have taking the photos were outside with the lens facing the ground so i think it probably
was the is causing the problem...i noticed before i sent it in it was when i had the camera lens down that it wouldn't take the photo and i did try that when i got it back and it took it fine...how long it works remains to be seen but didn't want to create a false impression about the aperture
one other caution imo you can't really compare a lens like the 28-135 with L glass that costs 3-4 xs as much..you get what you pay for to some degree so if it fits your budget, buy it, if you can afford L glass buy that. same with a prime, they usually are sharper but you don't have the range so you gotta pick your battles
