Nice, simple, functional. Does a single job and does it well.
I would second the suggestion for some extra layout options (particularly a landscape variant which would work much better for some areas), though take care not to go OTT or you'll complicate the nice simple interface and put off more users than you help with the changes. Perhaps have one or two extra options (the most significant ones like landscape/portrait) and hide others being an "advanced options" click. That way most people get the simple interface but those that want to be more fussy are catered for too. Though as always don't try to please everyone, the really fussy users will never be entirely happy and you are better off recommending that they produce their own posters by hand!
Also, do look into the potential licensing issues mentioned by anc84. Some effort here and now ensuring that you are compliant (either because you just are or by negotiating different use rights with these or alternate services) may save you a lot of hassle and expense later down the line.
I would second the suggestion for some extra layout options (particularly a landscape variant which would work much better for some areas), though take care not to go OTT or you'll complicate the nice simple interface and put off more users than you help with the changes. Perhaps have one or two extra options (the most significant ones like landscape/portrait) and hide others being an "advanced options" click. That way most people get the simple interface but those that want to be more fussy are catered for too. Though as always don't try to please everyone, the really fussy users will never be entirely happy and you are better off recommending that they produce their own posters by hand!
Also, do look into the potential licensing issues mentioned by anc84. Some effort here and now ensuring that you are compliant (either because you just are or by negotiating different use rights with these or alternate services) may save you a lot of hassle and expense later down the line.