While the mission's size can be explained by the fact that it was built for the Summer Speedbuild Competition, I think it's completely fine as it is (perhaps the outside area could be more detailed, but that's all). I wish more fm authors would consider building small sized missions (which you can finish under 1 hour), not everything has to be an epic 2-3 hours intensive thievery. I sometimes mind a bit that the more experienced and talented creators avoid thinking in smaller scale, but cons...
I guess if you are generally fault-finding and overly critical as a person, then very few fan missions will be satisfying to your standards. I have enjoyed playing this mission even during the beta phase. There are a couple of things I liked less, but for me it's a solid 8/10, especially since this is the author's debut.
Hmmm, I'm not 100% sure about the "beginner's effort" part, but I can definitely see what you mean by that. In terms of quality the mission isn't too consistent (also there are a few parts which kinda have an unfinished/abandoned vibe), but I think some areas were really well built in terms of annention on details, asset placement, usage of textures, etc. (not to mention the wild ideas of the second part)