I'm very happy with my Robinsons which we put up in 1991. The structure itself is tough enough to tie things to or hang a couple of hanging baskets from the cross beam, and the sliding doors are still functioning perfectly with no sticking. No guarantee of course that 2012 Robinsons are still the same spec.

Main recommendation is to get a greenhouse bigger than you think you will need. Mine is, I think, 16 by 10 and is too small. It has a partition part way along, so in winter I have a heated inner part and an unheated outer end.
The outer door is double, which is great for access, and for leaving open in the summer.

You'll need more opening windows than provided. Automatic vents on at least some of them. One or more louvred panels at the base improve ventilation, although I don't have those and it hasn't caused me a problem.

If you're going to heat it, think hard about what you will do with the area under the staging - if you're not using it for plants and therefore don't need the light, make a thicker insulated wall under there - it's not the biggest heat loss but every little helps. Make sure it's draught-proof, especially where it joins the base (and this will also stop water seeping in underneath).

If you're putting electric heating in, then add in an electric light, and a spare socket for your radio. A reasonably comfy chair is good too.