When Sega announced it had picked up the rights to the Thunder Force series in 2007 and that it intended to produce a sixth game in the shmup franchise, there was plenty of room for optimism.
For one, Thunder Force had become one of the premier shooter series of the '90s, with the third, fourth and fifth entries earning plenty of praise. There was also the fact that Konami (with the help of Treasure) had successfully revived Gradius for PS2 in 2004—proof that there was room for the genre to thrive on PS2.
Thunder Force VI ended up being a Japanese exclusive that earned a mixed reaction from fans, with one of the major complaints being that it recycled too much from previous entries. Its production values also came in for criticism.
Speaking to Time Extension, designer Tetsu Okano admits that the reaction wasn't ideal:
As for what didn't go well, not being able to live up to the fans' expectations was definitely one thing, and for that, I apologize. The responsibility lies totally with me, so I'm content to take any complaints.
However, he maintains there are some positives to be taken from the experience:
As for what went well, I'd say it showed that old games can be remade, depending on how you do it. (Back in 2008, there wasn't a resurgence of interest in retro games and indie games hadn't risen in popularity yet). Also, it was such a low-budget project that staff members would pay out of their own pocket for additional characters, but the project as a whole didn't incur any losses, so I guess you could say that was another thing that went well.
At the time of writing, Thunder Force VI remains the final entry in the series. Sega now owns the rights to Technosoft's back catalogue and enlisted M2 to produce 3D Thunder Force III on 3DS, and SEGA AGES Thunder Force AC and SEGA AGES Thunder Force IV on Switch.