Even though the Rockies have never won a world series (yet!) an evening game at Coors Field is something every Colorado resident and visitor ought to experience. Even if the game doesn't enthrall you, the beer, hotdogs, and stunning views of both the mountains and downtown will- especially at sunset.
Coors Field offers all the classic components of an Americana-rich baseball game. Food and beer vendors are abundant, occassionally even some peddling regional craft brews (all much better than Coors, in my humble opinion). Also the weather in Denver is nearly always warm and sunny in summer and fall, making this stadium particularly comfortable.
The infamous Rockpile seating section can always be counted on for tickets under $10 and plenty of rowdy energy.