Is the Fillmore a good place to see a concert?

Yes, it is open and has kindof a mysterious vibe with the purple lit chandaliers, I think its a good venue (small but big enough)

I haven't been there in years, but I remember it being a fun place to go!

It's a great vintage venue with plenty of room - definitely not one of Denver's smaller theaters. However, there are only a handful of tables / chairs (available upon reservation); the rest is standing room only.