It's incredibly basic and small, with boxlike, unimaginative corridors composing literally everything. It's designed to allow teams to spawncamp, since one of the routes out from mid does exactly that. The mid is uninspiring, stupidly sightline-heavy and not fun for any class to fight in. The vents are horrible and cramped, and don't really help at all with the campiness of the intel room like they're meant to do. The intel room is very campable, being right next to spawn with really tight and chokey routes into it and health and ammo everywhere for the defenders' exclusive use. The routing is pretty awful - when you push out of mid your two options are 1) attempt to spawncamp, wow, how fun or 2) push into the horrible, campy intel room. It doesn't even attempt to fix the fundamental problem of CTF as it's featured in the game, where your intel room is behind your spawn, so pushing forward leaves you vulnerable to getting backcapped, so you have to constantly camp your intel room in order to not lose. I never have fun playing as any class on Turbine, because who would want to play unimaginative tower defense in a map where no area is well-thought-out or fun to fight in for hours when you could instead play KOTH, PD or 5CP?
I firmly believe that symmetrical modes are best when the objective often changes hands and the 'front line' often moves as a result of that. You can see that in KOTH, where the point is captured often because it's easier to push than hold, and the 'front line' moves forward after you capture the point, because your team starts a forward hold. You can also see that in such modes as PD, where the deposit zone is locked until a certain amount of time passes, and points are always captured when the deposit zone opens, but the team which is winning in terms of points won't be able to capture points unless they control the deposit zone, so the deposit zone feels neutrally contested and fair. Both modes are very well-liked because of these attributes - that's probably the main reason why anyone who knows what they're doing makes Halloween KOTH/PD, because that's what Valve puts in the game nowadays.
CTF is meant to achieve this too, since the 'front line' is meant to move based on the position of your team's flag (when it's stolen, you're meant to hold forward to reset it), but it ultimately falls flat in that both teams have to stay at their base until their flag is stolen away, before they can push forward. In addition to this, pushing forward does not let teams forward hold (due to the close proximity of the enemy spawn to mid), so it never feels worthwhile to try, so both teams stay at their bases and the front line never changes. This is probably the main reason why people like Invade CTF and Chin CTF so much, because you don't have to stay back at the base to guard your flag, so forward holds are actually relevant and the front line often changes, so the gameplay feels fun and dynamic instead of feeling like boring tower defense.