From everything I've heard, the Sig 1911s are reliable pistols, but personally, I dislike external extractors on 1911s. Also, the Sig "1911" slide appears to be quite different from the traditional 1911 design. These and certain other variations (from other manufacturers as well) don't appeal to me on a 1911 style platform. YMMV, of course.
1911 mods that I don't find objectionable include:
-flared/lowered ejection port
-front strap checkering
-bobtail
-extended beaver tail
-upgraded sights
-extended safety and/or slide release
Objectionable mods:
-rails
-front cocking serrations
-external extractor
-odd barrel lengths (e.g., Kimber's/Springfield's 4" rather than 4.25")
-CCO configuration
-1911s without barrel bushing (I mean, c'mon!)