I struggled to get the Centre channel right for many years (going from a Sony, to a JBL, to a Tannoy, to an Acoustic Energy, to a Monitor Audio) and it's only in the last couple of years I've managed to get a speaker that integrates well with the front pair.
the Monitor Audio isn't perfect, you have to be in the sweet spot or you get lobing effects (as with all horizontal centres that don't have tweeter/mid and woofer on different axes on the baffle) but its the best of the 5 I've experimented with to date, so long as you're not way over to one side of the room, everything is fine, more than fine in fact, its great.
to my mind, the most important thing with centre speakers I've found out along the way is timbre matching it to Front L&R, for 5.1 the rears ordinarily make scant difference, with Quad, all 4 pref the same sonic signature of course.. all of which is most noticeable when I setup my Monitor Audio's, suddenly the centre is virtually seamless, just as it should be.
despite the technical difficulties of getting the centre to gel for music, I've always thought it to be a fun (exciting, even) addition when used well (though my favourite surround remix man of all time, Elliot Scheiner, doesn't use the centre much as a rule, I have to admit).
hearing Freddie's incredible voice in isolation in the centre, or the young Elton in his 70's heyday, or Marvin Gaye's glorious vocals is just spectacular. everyone I've ever played the magic trick on of solo-ing the vocals in the centre-only of these mixes has been utterly gobsmacked, spellbound even.
is that a gimmick? is it the ultimate extension of high-fidelity? is it as close to being in the studio/with the artist as possible? I don't know but its a bloody huge load of fun you can't do with 2-channels..!!!
oh and I should add, to kinda get back and leap to the defence of the legitimacy of the centre channel for surround music, that when you've nailed the timbre of the front 3, it can be superb... though I have to say some of the best Quads have got absolutely incredible phantom centres, you literally would have thought the centre was on!