Ulrikke
No more frogs
see, i think that him falling in love with buffy makes him more interesting, not annoying. because, even though he loved her, he still hated her--he still fought with her and wanted to kill her and just got more and more confused as time went on until he finally sorted it out in season 7. spike is great because of his complexity, because he could love her and hate her (what a thin line, anyway), because it made him way more paradoxical than just simply a badass.
I have to agree with you there. As much as I love the early "all-evil" Spike, it wouldn't be half as interesting to watch without the knowledge that there is so much more to the character - that a big part of "Spike" is essentially an act.
Also, there is such a thing as character development. If Spike had stayed the way he was is seasons 2-4, what would have been the point of keeping him around for 4 more seasons? Joss et al had to go someplace new with him and they did that by having him fall in love with Buffy. Love it or hate it, it brought his character to a new level. Imo they - for the most part - did it brilliantly. Watching Spike finding - and struggling with - his humanity was definitely one of the highlights of the entire series for me.