*warning this is going to be long... sorry :o)
personal opinion, the price is good for what your getting. an average 1ct round or princess would go for about 3,000 anyway so add another 1.44ct in white gold for 4,500 sounds like a deal to me however on the clarity isn't that great.
an I1 is in the lowest category on the clarity scale which means there will be visible inclusions (or some may say "flaws") inside or on the stone visible to the naked eye. the larger the stone the more visible the flaws. however, you can find an I1 that will be decent looking to the naked eye but you may have to shop around for that and compare I1 stones.
here's the clarity chart link: http://www.nitacreations.com/images/diamond_clarity.jpg
an I color falls in the near colorless range second to last which means the stone will have a slight yellow tint in it.
here's the color chart link: http://www.usajewels.com/online-store/scstore/images/diamondcl.jpg
the most important factor in a diamond is the diamonds cut (not shape) but the way it's cut. the arrows signify the light, so you want a diamond that reflects the light well in the diamond otherwise your gonna have a stone that looks dark (deep cut) or light (shallow cut) none of those cuts i just mention is something you want from your diamond. because, a deep or shallow cut won't reflect light well therefore giving you either a dull diamond or a dark diamond. the purpose of a diamond is for it's sparkle and brilliance. without that it's just a stone.
a well cut diamond will also mean deeper pockets for that matter because the better the cut the more value.
here's the cut chart link: http://www.treasuredjewels.com/images/diamond_cut_chart.jpg
here's the link that explains the 4 C's: http://www.helzberg.com/category/learning+guide/diamonds.do
although it's not my taste because it's generic looking i'd like something that would say it's more me. but you give her what you like and what she likes. that ring will also be a bit bulky also because the fact that it has a lot of metal around the channel set stones may take up a third of her ring finger. don't pay attention to the people that are saying this ring is too expensive and that they would never spend that much in the first place. my ring was over 8,000 and worth every single penny and absolutely satisfied and happy with it.
the link of the ring i have below is from bluenile.com which is a very reputable diamond website. the diamond and the ring overall is definitely better then the one your asking about. although it is about 500 more you are getting:
18k white gold bridal set
2.08 ct t.w
0.56 ct t.w. engagement mounting
0.44 ct t.w. matching diamond band
Platinum prongs for center stone
Minimum Diamond color: I
Minimum Diamond Clarity: VS1
GIA Certification
option for thinner set but similar style and weight: http://www.bluenile.com/design.jsp?filter_id=1
i hope this helps.