I bought this game in the year I bought my PlayStation (1998) and this was a huge mistake. Not because it's a bad game as such, but because this is not a game for beginners. I eventually sold it, but it's not a game I would shun, merely caution against.
The graphics are undeniably poor, even for its time. They're grainy and not very well detailed, and this can detract from the experience at some points, especially as some switches/items are hard to see. There is nevertheless an element of atmosphere associated with the visuals and this game manages to pull this off quite well.
The story isn't very prominent in the game, but I found the FMVs between levels to be interesting enough; your ship has crashed on a mysterious island with a tower on it. Your captain is missing and it's up to you to retrieve him, along with a mysterious artefact.
The game is much like Tomb Raider, but with a bit more looseness in the controls. You can choose four characters (plus two hidden), the only real difference between them being their starting proficency in each weapon type, plus the abundance of each type of ammo in the game
You have four weapons in the game; bolt gun, flamethrower, lightning gun, and light pillar gun (plus grenades and bombs), which may not sound like much, but each of them can be upgraded multiple times and the difference is noticeable. You can also cast magic spells. I personally rarely used magic for anything other than healing, but there is a fair number of spells at your disposal.
But now to get to what O. D. T. is most memorable for; its difficulty. Even on Easy, it is a very, very hard game. There's a lot of places to fall and die (a problem not helped by the controls), there are more hazards than you would ever believe and the save points are few and far between. To make matters worse, you can only access the last stages of the game if you play on Normal or Hard. Do Psygnosis enjoy watching us suffer?
If you have the patience, however, O. D. T. is a compelling game. The puzzles are challenging and varied, the boss fights are fun and exciting, and there's secret sections just about everywhere.
There are eight levels, but they are all long and treacherous, and, assuming you don't lose your interest in the game due to its difficulty, it'll take you a fair time to beat. Especially as you'll want to play on Easy first (no, trust me, you will) and then replay again on Normal to get the proper ending. But due to the number of secret areas, replaying should offer a different experience to the first time.
O.D.T. is a fun game that fell short of recognition due to its horrible graphics (and that it came out at the same time as TR3) and while it's a hard game, it's rewarding as a result. If you have the patience.