Tag should have been a stupid, pseudo action film which loaded all of the best bits into the trailer and skated on Jeremy Renner's star power. Instead, I watched a film with several laugh-out-loud moments, a surprisingly enjoyable "Sherlock meets Hawkeye" mashup character for Renner, way more heart than I had anticipated, and that was surprisingly based on real events. The bits they decided to embellish made sense, including the central conceit of one person being "untaggable" and the twist cancer ending, and in general the film's suspense actually worked, keeping you guessing at who was playing whom and what the ultimate point was.
In other words, Tag was a lot better than it has any right to be. It's still a largely pointless and silly film that doesn't stand up to any kind of plot scrutiny or application of physics, but it was self aware enough to joke about those elements and get a pass as a result. I enjoyed it quite a bit but will never go back for round two.