28-300L

How does this rank for wildlife / general tele work? The advantage being no lens changes in the field, even for landscapes!

Optics have never been great. Some argue that it is not even L series quality. Personally I could not sacrifice IQ over not having to change lenses.

Have a read up on it here. Does seem positive http://www.the-digital-picture.com …L-IS-USM-Lens-Review.aspx

Not too sure if Canon still service it though.

How close do you intend on getting?
I would suggest that, in the wild, you're doing great if you get to less than 30-40 yards and for that a 300mm is minimum to "fill the frame".

Yeah, you can crop and lose pixels...if you can afford to throw them away.
Critter pictures generally take long glass.
See my portfolio, those Great blues were 60 yards away and shot with a 300mm 2.8 with a 1.4 extender on a Ds3.
The panorama hasn't been cropped, pretty small huh