It's not. I hate the place, it's one of my least favourite stations. It's out of date and not designed for passenger benefit; a victim of 1990s cost cutting that nobody will properly fix. It's like old New St (which was, probably deliberately, a bit of a mini-Euston) but worse.
Yes, the tram bit looks a bit German and has some nice architecture (why does Metrolink get the best bit?), but the rest of it is just horrid. And the new plastic roof is just cheap and nasty (and leaks).
I'm not even that convinced about the building. It has a nice map and an olde worlde wooden ticket office. It's impractically shaped, the roof leaks, the new bit is like New St where someone's set fire to a massive pool of diesel, its main feature is a row of ticket barriers with a big ugly advertising panel above it (couldn't they just put something useful up there instead like a departure board?), it doesn't even have a main departure board, the toilets are absolutely disgusting (even worse since they became free) and it's served mostly by a third rate TOC. Add that it's freezing in winter. It's just awful. A third world mess. Literally nothing good about it.
It was borderline adequate when it basically just played host to local services. It is now TPE's main station (a grown up TPE which is much more InterCity than previous instances of it), and for that it is downright unacceptable.
If the Arena fails when the new one opens, and I really hope it does, it'll be a great opportunity to flatten the lot (other than the small fancy building) and rebuild it to proper European Hbf standards.
Piccadilly, by contrast, 13/14 aside, is a wonderful station. Great facilites, light, airy, nice architecture etc. Feels like a proper big-city Hbf.