I can certainly understand your frustration. 'Semi-Pros' advice is very good. I'd like to add a few more things to consider.
Picture yourself being the judge in small claims court. What's he gonna want to see from you to make your case? Pictures of parts of the good job he did, and pictures of ALL the bad parts too (not just 1 or 2), plus and cost estimates from Wallpaper Professionals (not just 'any' contractor) to re-do the job. Admit, like you say, to those things about his work that you can live with (show a picture). This shows the judge you're being reasonable. And, unless you have a trained eye, are you going to see the 'bad' work? It would be reasonable to consider what an untrained eye might see and go with that. You shouldn't have to live with that but just think about what's a reasonable 'thing' to live with. And lastly, document EVERYTHING! Write down every time you called, left a message, discussed what with him, length of conversation, date, time, and on and on. And lastly, he must be given the opportunity to fix the job. If he's not going to cooperate, thank him and let him know that your husband intends to seek damages to rectify the problem(s). At the same time, have you checked with the Better Business Bureau(BBB) in your area? They may have something for you to take to court.
I just want to suggest that if you plan on any future custom-type of work, seek out a few installer-references from those professionals that SELL you the product. I know you wouldn't go to the local tavern for free legal advice and you wouldn't call a plumber to do electrical work (although he's very familiar with how water and electricty don't mix). I don't mean any disrespect out there to those professionals who are well-skilled in multiple trades. Personally, I've done vinyl siding a few times and am comfortable with it but I wouldn't do my neighbors because I want to stay on speaking terms with him. In short, from all you've mentioned about all the 'little things' in this kind of job, I'd have gone out and gotten a professional paper hanger. Hinde site is 20-20 (I think I've lectured enough. You've got your problems.)
I sincerely wish you well and you've gotta do what you've gotta do. Be prepared for court and get the 'right' professional for the task. By the way, welcome to the I Think I Got Taken Club. It's NOT very exclusive. :)