Just to get one thing straight from the off - I am a jrpg fanboy and my score probably reflects this! Trinity Universe is a turn-based traditional style Japanese role playing game. This means that the cut scenes will be basically static portraits of characters exchanging a lot of dialogue - most of it pretty whimsical. The story will be silly and there will be an expectation to level-up all your characters a lot and collect a lot of loot.
If this is not your type of game then you are probably not going to like Trinity Universe. The game has some small changes to the traditional style - the static portraits include a bit of animation to make them look like they are breathing etc, but it isn't fmv in any shape or form. The sprite graphics of previous games have been replaced by 3D cel-shading, but are still a long way from glorious hd graphics of games such as FFXIII. However, this still gives the game a unique charm (if you like that kind of thing) and the gameplay is still pretty deep.
The gameplay is basically split into 3 areas - events, exploration and battles. Events basically play through the various dialogue for the story - they do tend to go on a bit and there are a lot of references to previous games in the genre. Exploration means accessing the dungeons on accessible orbiting objects and involves a 3D 3rd person exploration. You can use a search function to highlight hidden objects and you have random battles to face - these can be halted for a while by completing the hunter challenge. There are bosses to fight and Lurkers, who are mega tough enemies that can hunt you down. Also there is loot to collect and you can get rare loot by destroying the gravity core and picking stuff up before the time runs out.
This is one vital element to exploration. The objects drift in and out of the orbit of the planet and you get a warning if you are exploring an object that it is about to leave orbit and you have to get to the exit before the time runs out or float off into space and pay to get rescued. It certainly adds a bit of pressure to exploration, which I like.
The battles are turn based. The order of turns for your characters is set up in the menu so you know who is going first. The combat itself is based on 3 attacks and an special action. The attacks are a rush attack, a mega? attack and a magic attack. These can be used in combos to unlock special attacks. After you play a while you can also combo with other characters to unlock multi character special attacks - but this can be tricky as it depends on your timing. You obviously get exp and loot from winning battles . The characters level up automatically and you have no control over stat increases or new skills gained - this is possibly the most disappointing thing about the game; but is also in line with a lot of traditional jrpgs. The battle system is complex enough to provide opportunity to try different strategies and is certainly the best thing of the game.
You can synthesis new items/weapons/armour and you can pimp your weapons with manographics that add special abilities. The equippable items also provide stat increases and special abilities and so you have indirect control of upgrading your characters and choosing which attacks to focus on.
Outside of the main gameplay there are shops and a monster arena that allows you to synth monsters to fight to gain exp etc. The monsters you fight and items you collect are also dependant on time of day and day of the week so you can visit the same dungeon at different times to get different items.
To conclude, it really does help if you are a massive fan of these types of games - especially the disgaea and artelier series. If you are a fan then the game is excellent and meets the needs of an indepth jrpg experience and you will tend to overlook the strange design choices - because you are used to that kind of thing! You will enjoy the move to cel shading and appreciate the tongue in cheek humour of the box describing the animated cut scenes.
However, if you a do not enjoy these type of games then you are not going to get over the various flaws of the game and things like no character customisation, the repetitive bgm, the clumsy graphics, archaic inventory management etc will put you off. It's a shame because the game does develop over time and I think it overcomes these faults to provide an awesome experience that is different to many other games out there.