What makes a good second loop? What games have good ones?

[Cthulhu]

I just 1CCed Twin Cobra (1CC on the first loop only ) and I was really impressed with what they did with the second loop. It gets ungodly hard (big suprise there), but it changes the game up a lot. The enemy layout changes a good deal (lots of new popcorn helicopters), the positioning and frequency of point items changes, and there are new bosses! The levels are the same, however, so it's obviously a loop.

What makes a good 2nd (and 3rd, and 4th...) loop? To me, death bullets are a pretty cheap way out... adding in nothing more than those makes a second loop feel really hokey. Even more of a copout is not changing anything. (Although not shmups, Contra and Super C are the first games that come to mind that don't change subsequent loops at all. I'm sure I've played some shmups that don't do anything new, however.)

Adding lots more bullets and changing up the patterns some (ie: Dodonpachi) is definitely a step up from that. Severely changing things like Twin Cobra is also really neat.

Any opinions or games that come to mind?

[Sly Cherry Chunks]

Content, plain and simple. Increased difficulty, sure but anything like the second core on that Gradius V boss or different colours on the second loop of R-Type III is good in my books.

[D]

Gunbird 1 and Zero Gunner 2 have different background color pallets, perhaps all psikyo shmups have this.

[Icarus]

Raiden DX.

If you clear Training Mission without dying, bombing, at least 99% of enemies destroyed and with at 100% secrets, you'll access the "second loop" which is actually the next mission up - Novice Mission - at a higher difficulty. If you manage to clear this "second loop" with the same requirements, I believe you access the next mission after that - Expert Mission - at "third loop" difficulty.

I quite like this style of looping. It's like being assigned new missions after expertly clearing the one you've done. So far, I've come close to clearing the "second loop", but it's very difficult later on in the game, with fast firing sniper tanks and boats