BIG FAT GREEK DISCLAIMER: I am NOT trying to start an RSG vs. Iky debate here, nor am I even directly addressing any gameplay elements of either title aside from how "accessible" they are: PLEASE do not interpret this as anything other than personal observation, as it relates to the aforementioned! That said...
While both games are similar in a number of ways, including their emphasis on a "chain" scoring system, ridiculously overbearing backstories and a very high difficulty level, I've come to find Silvergun, despite how much of a challenge it offers to gamers of all skill levels, to be more immediately "accessible" (though not innately "better" or "worse") than Ikaruga in many, but not all, areas. Here are a few reasons I think this way:
1) Options. Even before you get into the gameplay itself, RSG offers more ways to tweak the game to your liking, in either direction: IIRC, it has 5 difficulty levels to choose from, while Ikaruga has 3 (though it is worth noting that Ikaruga's difficulty levels affect mainly [only?] the "suicide bullets" present in the game, while RSG's affect difficulty in a more "traditional" manner). Also, again IIRC, while Ikaruga allows players to have up to 5 lives per credit, RSG allows up to 10. These allow newer players to last a bit longer when they're getting used to the game, and get a bit more practice in without having to start over every few minutes.
2) Scoring System. Both games make use of a "kill 3 enemies of the same color to score more points" chain system, and both offer accessibility advantages in this area: in Ikaruga's case, there are only 2 colors to sort out for chaining purposes, as opposed to RSG's 3, and in addition, the former allows (and encourages) players to alternate in blasting "trios" of enemies to keep the chain going: for instance, you can shoot a trio of white enemies, and then a trio of black enemies immediately following that, and the chain will keep going. In RSG, you are forced to stick with one enemy color throughout the entire stage, which allows players less freedom to work chains out, and also forces them to leave more enemies alive to shoot at them, for the sake of keeping their chain going.
On the other end, though, Silvergun also offers accessibility advantages in its scoring system: first and foremost, while Ikaruga makes chaining almost the only thing players can do to substantially increase their score, RSG offers other options therein, such as weapon bonuses, "secret" chain bonuses, Merry dogs, and boss destruction bonuses, all of which are, at least IMO, a good deal easier to get the hang of than chaining is, though not as lucrative. To be fair, Ikaruga also offers a bonus for killing bosses quickly, but since it only has one boss per stage as opposed to RSG's several per stage, it doesn't close the gap between itself and chaining as effectively as RSG's boss bonuses do.
3) Modes. In Ikaruga, aside from adjusting the difficulty as mentioned earlier, the game doesn't offer you many options to change its inner workings much. RSG, on the other hand, offers Saturn mode, in which you can save your powered-up weapons from game to game, and eventually become well-armed enough to finish the game if you're persistent enough, even if you haven't mastered the game's scoring system yet. RSG also offers an eventually-unlockable "slowdown" mode in which the game plays slower to give players an easier time to practice (I believe that the US release of Ikaruga also included something like this, along with a "replay" mode not available [AFAIK] in RSG, but the original DC release didn't).
4) Misc. As far as loose ends go, I might also mention that on 2P mode, it's much easier to tell the 1P and 2P ships apart in RSG than it is in Ikaruga, though in the latter's defense the game's whole premise makes that rather unavoidable. In addition, RSG's "Hyper Sword" is easier to direct toward a specific target and offers a longer invincibility window than Ikaruga's homing laser does.
On Ikaruga's end, it only forces the player to learn 3 buttons, as opposed to RSG's 7 (yes, technically you can get away with 3 on RSG, but that's arguably even harder to do), and also, while its weaponry isn't as impressive, doesn't give the player any real power-upping (aside from the homing laser) to worry about, so at least the shots you do have stay consistent. Finally, of course, Ikaruga is a good deal shorter than RSG is, making it a less grueling journey for a newer player to fight through.
That's about all I can think of offhand to exemplify what I'm saying...again, I'm not trying to say that either game is superior or inferior, "period," but am only comparing them in terms of how "accessible" they are, and even then only in my personal view. I wouldn't doubt I made an error or two up above, and if I did don't hesitate to point it out (as if any of you would anyway, heh
) So what are your thoughts on this whole issue? Is accessibility a good thing since it allows players to get into a game more easily, or a bad thing because it can make the game "too easy?" Is there some sort of "happy medium" that developers should aim for? Or does accessibility even matter to you at all, or do you simply take a game on its own terms without even considering how much "breathing room" it gives you? Or is the value of accessibility determined by the player who uses it? I'm interested to hear what the rest of the community has to say on this...just PLEASE, don't turn this into anything hostile, I'm just looking to see what people say about this, not trying to get everyone to unquestioningly agree one way or the other. That said, let loose, heh.
There might be a shmupper on this board that has never played the saturn RSG(arcade only!). I think we should avoid comparing arcade version with their console ports to avoid confusion. 
