Before I go into objective details, I will just put this out there and say this. From the bottom of the card to the top of the card, TNA's themes are bland, generic, and sound like they should be on an N64 version of No Mercy (and even that game had better entrance themes than TNA's actual show). The ONLY entrance theme in TNA that is catchy and very original is Pope's, and they (or maybe it's Elijah/Pope's idea) deserve a pat on the back. Only my opinion, on to the meat.
The main difference between TNA and WWE's themes are a few different things :
Job squad to Lower/Mid Midcard - Most of TNA's themes are just generic guitar/hip hip/techno riffs that have absolutely no imagination put into them. They are just background noise and in no way match the actual character using them. WWE puts more work into their themes, but sometimes really flop, for example, Ziggler's theme. It sounds like TNA was actually sourced to do this theme for him, lol.
Upper Midcard - Main Event : Discussing names that don't come from WWE (where they blatantly take ideas or outright copy the song), again, it sounds like an amateur sound team picked up a guitar and synth, made a generic riff, and threw in some special effects to spruce it up. WWE on the other hand, shows where they rise above TNA in this area.
WWE has the actual money to call up a band and pay the guys for rights to use their music on WWE Television for any given superstar. Most of the Upper Mid Card have sourced songs from major bands that people recognize. Guys Like Triple H and Edge actually have REAL bands customize a song for their entrances, which REALLY sets them apart from any of the status quo. Triple H is the best example, every single entrance he's had has been motorhead since 98. King of Kings is still one of my favorite WWE entrance themes of all times.
TNA just needs to open their eyes and see that entrance themes do ALOT for a character. Pope D'Angelo Dinero is the best example going. For anyone who didn't know who he was, the moment that funk hit the speakers people were interested. It's a GREAT FRIGGIN' entrance theme. I don't know why TNA doesn't see why Pope's entrance theme did what it did, but all it took was two appearances and you had the marks firmly behind him, because his entrance theme made him look legit, and bigger than life.
Every other TNA star has generic music that does nothing for their character. I hate Kurt Angles theme, you can hear where they outright stole his WWE trumpet theme, and Hogan's NWO theme that was ACTUALLY taken from a WCW N64 game sounds like complete garbage. Can't really say much for hogan, because Vince owns BOTH of his entrance themes from WWF and WCW, so Hogan's pretty much stuck with using cut-rate music that sounds hand-me-down and cheap.
If TNA were smart, they'd source out a lot of entrance themes to popular bands, and they'd see instant returns in stars getting over only because their entrance theme kicks so much ass. That, or hire a MUCH better sound team than what they have, or an outright totally different division dedicated to engineering and creating good opening themes for all the stars.
TNA also doesn't realize that it isn't as expensive as most people would think to buy rights from a band to use a song. This is HEAVY advertising for the band. WWE gets extremely good deals when they procure a sourced song from the band, because the band knows millions of people will be hearing it on TV, on PPV, and of course, on WWE Soundtrack Albums. It's a win-win-win situation for all parties involved, WWE gets an entrance them, the band gets next to free advertisement for their material.