Personally I never liked the kidnapped girl plot in t3, you had no idea who that mia woman was or what really she had to do with the machine, it all seemed a bit random.
I actually did start writing a full scale Turrican novelization at one point. In that, Bren Mcguire was actually something of a failure, sinse he'd been involved in a doomed expedition to a planet with an acidic atmosphere, ( actually like the hard woods environment from T4 funeral).
Colonel Striker ended up pretty much forcing him to go on the mission with the avalon 1, because they needed a third Turrican suit operator. Mcguire didn't get on with the other two suit operators, mostly because he was bought in at the last minute as n outside choice and because Colonel Striker was a friend of his father's.
The story was also an attempt to link together t1 and t2 plots in a much more coherent way. The reason however I never finished is I realized I'd pretty much need to write an entire thousand year galactic timeline, between the appearence of the vil evill moon in Earth's solar system in 2086, the defeat of morgul in 2090 by Turrican (actually Adam Turricano, the first genetically modified human born off earth), and after various colonizations, wars across the solar system, contact with aliens and the like, the events of T2 happening in 3025.
The final revelation was that the machine was actually the original Turrican, who'd stolen the ship from the evil moon and arrived wherever all that technology came from, and he was altered to live a thousand years and finally ride a second evil moon out to planet Landorin and carry out the invasion. The implication was that because Turrican was pretty much abandoned by everyone once he landed on the evil moon and took out Morgul, he got rather irritated with life in general.
the final end was going to be Mcguire leaving the evil moon around Landorin to go wherever the moons came from, but with the implication that because he was a very different person from Turrican, didn't believe himself to be better than others etc, he would succeed in destroying whatever was behind the invasions and surviving whatever process had turned Turrican into The machine with his humanity intact.
I liked some of the random ideas I came up with for the story, in particular the vunesians, a race who didn't use science but just comprehended different things directly, and the idea that the Landorins were actually a colony of humans from the criogenic colonization ship Lamda.
I also rather liked the history of the first Turrican suit, something which actually could only be operated by someone with genetic enhancements because of the coordination required.
I don't know if it'll ever get done though sinse as I said the amount of background required for the plot was huuuuuuge!