This campaigning rock opera is a tricky show to review – in fact, it's a tricky show to get your head around. It's overflowing with big concepts, from the possibility that we're all living inside a computer simulation to a sinister suggestion of deep-state interference in political life. It's built around some fascinating ideas, and features some strident, provocative songs; but it's also a tangle of thoughts and themes, from which it's hard to pull out any specific message.

The plot revolves around a man, known as "Trim Tab", who wakes in hospital in Greenwich with no memory of his past. He's in the care of a psychologist – a slightly shady figure, who clearly has an agenda of her own – and at her suggestion, he attends a protest march, before diving head-first into the political scene. Before long he's penned his own manifesto, and has the whole country rallying to his cause. At first this seems implausible – why would Trim Tab succeed where so many would-be revolutionaries have failed? – but keep watching: it makes a cryptic kind of sense by the end.

The story's punctuated by original rock tracks, which aren't so much a part of the story as an adjunct to and commentary on it. Some are unashamedly campaigning: Better Together is an anthem for Europe, while Kids on Strike celebrates a political awakening among school-age children. Others are more introspective, like Go Deeper, which illustrates Trim Tab's struggle to understand his own mind. All are bold and soulfully delivered, with James Mannion as Trim Tab accompanied by a live five-member band.

Projected videos accompanying the songs are fascinating in themselves; you might see a montage highlighting the different shapes and sizes of animals' brains, or a mesmerising animated map showing the changing borders of Europe. But some of these, unfortunately, are so interesting that they distract from the songs. The track called M.A.N.I.F.E.S.T.O. suffers particularly from having a wordy proclamation – central to the plot – projected onto the screen in the background.

At one point, Trim Tab points out that protest is more effective if we "unite behind a single clearly-defined idea". It's ironic, then, that I think the show itself has a few too many ideas in play: we have ruminations on politics, doubts about the nature of reality itself, and towards the end a kind of deep-state conspiracy. Any one of these stories could be intriguing; together, they risk drowning each other out.

My other criticism is that, for a show that describes itself as "musical theatre", there isn't actually all that much music. The running time approaches two hours, yet there are only nine songs, and the first act is particularly heavy on long expository scenes. In part, that's because the complex set-up takes so much explaining. Simplifying the story could cut this down to a lean and mostly-sung 75 minutes, and the show would be better for it.

You can't fault the ambition of The Manifestation of Trim Tab Jim – and many in Brighton will applaud its grassroots brand of political campaigning. It's a touch unwieldy and a bit too wordy, but there's no shortage of things here to listen to and think about. The programme says this is the second part of a trilogy; I'm certainly looking forward to seeing how the story ends.