That's partly my point, this ride looks distinctly 'average'. The only reason the characters look like a good fit is because they look somewhat similar to what you would get from the show, that a certainly nothing special. There is no real sense of entering a underwater adventure of any kind, in fact there is no water.
It would have been good to see some animatronics, water elements. It would have been great to see actual on ride screens instead of stickers, with on board video explaining the mission. Just seems they have settled for the minimum which is a shame.
On-ride screens would be pointless. The weight of the tech and power on a coaster this size would cause issues. Small children would also then be either watching everything go by on the ride and ignore the screen or even worse watching the screen and not enjoying their first coaster.
The theming looks fine. It's the concrete floor they need to work on covering in my opinion. But that could still happen, even if just painted.