That's not a bad deal for that laptop. MSI laptops are alright, I've read and agree with the statement that MSI is above Acer but below Asus in quality, this is the "poor boy's MacBook Air". I've been happy with the MSI CR600 I bought last year, they're no Lenovo but the quality is decent.
Reviews on the older X320/X340 models were glaringly negative regarding the incredibly flexible and cheap quality keyboard, some reviews stated it was the worst keyboard they had ever seen in a laptop. Maybe they've fixed that problem in this one (you could probably fix it yourself with double-back tape if it was an issue).
What it lacks compared to the MBA (mainly processor speed, weight, and arguably quality) it makes up in having more usable ports (one additional USB, and HDMI) compared to the MBA's very limited array of ports. The SU3500 won't quite beat an Atom 330 in performance, it is pretty close, at a listed TDP of 5.5w compared to the A330's TDP of 8w perhaps that small performance difference can be forgiven. Single core Atoms will be left at the starting gate, Yonah Core Duos, Pentium Dual-Cores and Core 2 Duos will leave this thing at the starting gate ... But then again ... 5.5w TDP.
EDIT: Oh yeah, 3 year manufacturer warranty on this laptop.