I haven't yet had a problem with the raincover being too small, but my DD is only 18 months. The hood does click in place but not like others do, it's at the end of the hood rods, they click in at the side of the seat. The hood is one thing I think really can't be faulted on the oyster, it's by far the best I've used (and I've had a few pushchairs!).
However, the suspension is one thing that's annoying. I bought mine over a year ago, but it was an older batch. I had heard that they'd since fixed it, so it's a shame to hear you've seen it too (unless it was a long time ago, before the apparently changed it?).
I do think the oyster is great, and good value for money, but there will always be something better available for more money. My sister has a Joolz Day and Bugaboo Gecko which are both lovely to push, but then they're more expensive and don't have the nice fold like the oyster. I love that the oyster folds neatly with the seat facing either direction. I personally prefer it folded with the seat parent facing as it's a neater shape to lie in my boot and makes it easier to get 3 pushchairs in my boot. I love the hidden uv/insect net, the deceptively spacious shopping basket, the telescopic handle, the easy almost flat recline, how you can change the colour on a whim, the list goes on!
I'm really glad I bought it and the only reason I would sell it is to get an oyster max I think, assuming it has a nice push.
If you do get it, I wouldn't bother paying extra for the oyster footmuff or apron as they're both pretty short. I've ended up having to buy a new footmuff well two actually, one for each coloured hood.
Have a look on best buggy for an honest and unbiased review. 