Some thoughts on each mode:
Arcade HD: This is a really faithful port of a challenging, fun game that is flawed by a scoring bug ("overflow bug", as it is called). The port gives an option to fix this, which is great, but there are no separate leaderboards for "fixed" scores, which is not great. It reminds me of the lack of leaderboards to distinguish between 1.00 and 1.01 scores in Muchi Muchi Pork. Overall this mode feels like Mushihimesama Futari 1.0(1). A tough game light on score, with the scoring system not fully fleshed out. I've cleared it with the bonus character Saya (Type D), but I'm still working on clearing it with a "normal" character. I'm mainly playing as A-Shot, though I also like C-Laser. I can get to stage 5 regularly at the moment. Expert type is very challenging, and not something I intend to delve into any time soon.
Ver 1.5: The definitive version of Dodonpachi Saidaioujou. It's quite a shame that this never got an arcade release, but hopefully top players will score attack it in the port. It fixes the overflow bug, makes hypers charge quicker, and makes it much easier to restock hypers right as you end a hyper. This makes previously somewhat mundane sections of stages much more enjoyable, as you can plan out new hyper-based scoring routes instead of just non-hyper chaining. There are numerous other tweaks in the mode as well.
Novice: I have to say this is quite a nice Novice mode. Perhaps the best in any Cave game to date, though the recent Mushihimesama X360 port had a good one too. In Shot and Laser types, the difficulty is on par with Mushihimesama Futari Ver 1.5 or BL Original mode, but without the harsh increase in bullet speed in the later levels. Expert type is on par with a typical Cave Maniac-type mode. I think a lot of people will gravitate to this mode, as they may find Arcade or 1.5 too overwhelming in regard to difficulty.
Xbox 360 mode: A sort of interesting arrange mode. You can do a double attack as in Daifukkatsu Black Label (hold Shot+Laser), which instead of increasing a rank gauge, decreases a numerical gauge in the upper right (which starts at 10,000). You have a life/bomb gauge at the bottom of the screen. Both gauges are connected, so if one goes down, the other one does as well. You get them to increase by collecting star items during a hyper. Pretty fun, for awhile, but I wish you could play as the other 3 ships instead of just the new one.
Here is some information on the differences between Arcade/1.5/360 (translated from here):
Hyper differences
Level GP bonus Rank increase Duration% ACHD/360 1.5 All Modes ACHD/360 1.5 1 1.1 2 1 100 50 2 1.2 2.2 1 100 60 3 1.3 2.4 2 100 70 4 1.4 2.6 2 100 80 5 1.5 2.8 3 100 90 6 2.2 3 3 100 100 7 2.4 3 4 100 100 8 2.6 3 4 100 100 9 2.8 3 5 100 100 10 3 3 5 100 100
Laser usage differences (hits per frame per hyper level)
ACHD 1.5 X360
Hyp-Level Frames Hits Frames Hits Frames Hits 0 21 1 11 1 21 1 1 20 10 5 5 2 10 2 19 10 5 6 2 11 3 18 10 5 7 2 12 4 17 10 5 8 2 13 5 16 10 5 9 2 14 6 6 20 4 10 2 20 7 5 20 4 10 2 22 8 4 20 3 10 2 24 9 3 20 3 10 2 26
10 2 20 2 10 2 28
Star item base values
Type ACHD 1.5 360
Small-Air 100 100 100
Big-Air 1000 200 200
Small-Land 500 100 500
Big-Land 5000 200 5000
Notes: The current GP bonus is added to the values of each base value. In Ver 1.5 the current hit count x10 is also added to this value.
Number of hits added by each item during a hyper
ACHD 1.5 360
Hyp-Level: 1~5 | 6~10 1~5 | 6~10 1~5 | 6~10
Small-Air 1 2 1 2 1 1
Big-Air 5 10 2 2 5 10
Small-Land 1 2 1 1 1 1
Big-Land 5 10 2 2 6 12
Bomb Maximum differences
Arcade HD: The point value is calculated by 2222 x Bomb Maximum Level. This is added to your score at different per frame rates, based on the Bomb Maximum Level:
Level 1: Every 3 frames
Level 2: Every 2 frames
Level 3: Every 1 frame
Ver 1.5: The point value is calculated by 2222 x (Rank/5 + 1) x Bomb Maximum Level. This is added to your score at every 1 frame, regardless of Bomb Maximum Level. So, for example, if you are at Bomb Maximum Level 2 and your rank is 8, your bonus per frame is 2222 x (8/5 + 1=2.6) x 2, which is 11,554 points per frame.
Bee item differences
Arcade HD: The hyper gauge increases based on the value of your hit count when you collect a bee. Each 50 hits increases the gauge by 1%, up to a maximum of 30% per bee. When you collect the last bee in a stage, you get a 100% bonus on top of this (which equals one extra hyper level).
Ver 1.5: The hyper gauge increases based on the value of your hit count when you collect a bee. Each 200 hits increases the gauge by 1%, up to a maximum of 100% per bee. When you collect the last bee in a stage, you get a 100% bonus on top of this (which equals one extra hyper level).
360: Unlike the other two modes, your hyper gauge does not increase when you collect bee items. Instead, you get the point value of the bee item as follows:
Shot: 1000 x MAX hit value
Laser/Expert: 10,000 x MAX hit value
Also, when you get perfect bees for a stage the last bee's value is doubled.
Other notes:
-In Ver 1.5, Rank plays a role in the amount of hyper gauge increase per star item: at Rank 50 the gauge increases are 1.5 times that of Rank 0.
-Enemy point values are different across all 3 modes.
-You can't score on or milk bosses in any mode.
-Hit count does not affect hyper gauge increases while using the laser in 360 mode.
-Novice is the same as Arcade HD in all matters discussed above.