I'd say yes, absolutely Glenn Doc Rivers is a great coach. Here's why:
1. One Banner and One Finals appearance since 07-08.
2. Other "Probable" Finals appearances and Banner 
   opportunities were thwarted by none other than injuries 
   (Perk, KG, Rondo)....
3. If we remember to just last summer - Doc Rivers was
   heavily rumored to be a candidate to coach the US Men's
   Olympic team in the future - along with Greg Popovich - 
   another Great coach.
4. Someone name me another coach or team that has had to
   deal with the revolving door of personalities...egos...
   talents...that have come through BOS over the years:
   Marbury (08-09). The Blog, if I remember, almost
   imploded at mention of Stephon Marbury in Green. It 
   happened, and the man performed admirably...even doing 
   exactly what Doc said he would do "Marbury will help us 
   win a game in the post-season (and he did just that).
   No other team would touch him, but he did well in BOS.
   Shaq. Doc got the last bit of good health out of the Big
   Shamrock right before the Big Fella just couldn't play
   anymore - and BOS looked unbeatable with Shaq....and Doc
   made it work.
Not to mention a constantly changing bench (PJ Brown, Posey, TA, Big Baby, JO, Sheed, Nate, etc, etc...
Doc's dealt with it all, and at the same time has kept BOS
as a contender for the last few years. Plus, he's done an OUTSTANDING job monitoring our older player's minutes (KG, especially).
For these and other reasons I'm sure have been mentioned here already, Glenn Doc Rivers is a Great Coach.