Following on the heels of the successful Alpha 1, SRW Alpha Gaiden starts out just tying up a few loose threads from the first game. Namely: dealing with the Titans and glossing over the Endless Waltz plot for Gundam Wing. But then, as most anyone knows by now, Shu Shirakawa sends the heroes into the future and things get... different.
SRW Alpha Gaiden continued the process of modernizing the franchise's core gameplay and it marked the inclusion of Support Attacks and Defends, as well as getting rid of the annoying Limit stat and unifying weapon upgrades. It also kept route splits to a more manageable, actually told you when you got a battle mastery (and they were a little more sane now too!), and gave us New Game+ for the first time. Those were the steps forward... but they came at a cost.
Alpha Gaiden is tremendously much more tedious than the original Alpha 1, especially in the lategame. Bosses restoring their health happened only a handful of times in the original Alpha, but here it's the norm once you reach the Turn A Gundam finale, and they tack on stuff like Iron Wall which entirely kills any momentum you had in wearing down their health. I can understand this was implemented in response to being able to one-shot so many "tough" bosses in Alpha 1, but it's overreacting. And units overall are much weaker too, further twisting the knife.
And then there's the handling of various plots too. Gundam X is heavily, heavily twisted around to practically just be a footnote for Turn A Gundam, and Braigar's plot also just goes nowhere too. The inclusion of plot for Getter Robo and Great Mazinger is okay on its own, but it makes their plots in Alpha 2 feel like retreads and rightfully so. On top of that, the shortage of space-based missions makes most Real Robots much weaker too... and a lot of the better ones are locked out unless you're playing on the easy difficulty setting.
Of all the Alpha games I actually feel Gaiden is the weakest due to various changes from Alpha 1 that lead to a slower-paced, more tedious game. Graphically it's an improvement, don't get me wrong, but I'm glad that Banpresto mostly learned its lessons from this game once Alpha 2 came around. It's the easiest of the Alpha games to get into since it's translated, but it's also the least satisfying to play.