If you think about the plot of SMT II in a symbolic way parallel to The Bible, the Law ending is this. YHVH represents the laws of the Old Testament, and by defeating him, you usher in a new age of law, as in the New Testament, bringing salvation to the humans of Eden. In other words, Aleph is basically Jesus with a personal troop of legendary demons at his side.
Earlier, you go to confront the Elders of the Center. You end up fighting Uriel and Raphael at the same time, then Michael, and then finally YHVH Himself. Granted, that YHVH was a fake, but it's stated that He still had a ton of power, anyway.
Aleph is widely considered to be one of the strongest Shin Megami Tensei protagonists for very good reason. For example: the Archangels in the previous game were all in the final dungeon, and Michael in particular was a potential Final Boss and the single highest level in the game. Later, in IV, they're late game Bonus Bosses. Here? One is The Unfought, and the other three are mid-game bosses. Then there are the last three major bosses. Lucifer is generally the Final Boss, True Final Boss, or Bonus Boss. Here, he's a Trick Boss to YHVH. His Law counterpart, Satan, is particularly infamous for being one of the two toughest Bonus Bosses in JRPG history, but still ends up second to YHVH. And YHVH Himself? Excluding the second Famicom game, He never shows up to fight in one of His purest forms in any other game. Here, however, Aleph goes to Him and defeats him. The only downside to Aleph is the implications that YHVH came back and got his revenge, but in terms of achievements, Aleph has few rivals in the franchise.