Sigrun is simply an amalgamation of all the Valkyries you have fought in the original game. She thus feels less unique and epic because her moveset, timing, and overall behavior are very similar to the other Valkyries. She's just a stronger version of them with all of their abilities. Her design is also just like theirs but more regal to signify her higher status.
Malenia, on the other hand, is one of the most memorable bosses in terms of character design and lore. No other boss plays anything like her and she is a brand new challenge, not merely a suped up version of another enemy.
With that said, I don't find Malenia to be a particularly good boss mechanically. It's clear as day that Miyazaki and From's goal there was only to cheat players who were shouting from the rooftops that From's games difficulty is overrated. What did they do? The designed a mechanically unfair bosses with several questionable decisions.
- My main complaint about Malenia is that she punishes shield users. If you've gone through the game with a shield and face her, you'll have a much harder time than someone who is accustomed to dodging. That she heals health on shield hits makes absolutely no sense, but Miyazaki had to fuck over shield users somehow, otherwise, they could just turtle behind their high Guard Boost shields and slowly whittle her health away by poking her. Punishing someone this late in the game for using a perfectly viable build is nonsensical. That'd be like making a boss heal every time you dodge. Utterly stupid.
- Waterfowl Dance is a garbage move. I had to look up online to learn how to dodge it and it's the most counter-intuitive shit ever. Run away until the first flurry, then roll twice towards her to avoid the second flurry, roll away to avoid the third, then stand still so she can fly over you and miss you with the fourth. Seriously, what the fuck is this shit and how are we supposed to figure it out on our own? I wouldn't mind if the move was lightning-fast and required precise timing, but this isn't the case. It's just unintuitive with no clear indication on what to do when she starts it. You just gotta roll around and pray that you have enough health to survive the onslaught. If she starts spamming it, GG. A lot of runs aren't decided by the player's skills but simply where they were when she decided to whip out Waterfowl Dance 2-3x in a row. Thankfully, I got the timing and directions down now and take minimal damage. I can also destroy her consistently and quite quickly with Giant Hunt on the Great Sword.
tl;dr, Malenia is a cool boss visually and in terms of lore. The fight can be quite fun but From really got their heads far up their asses when it comes to their reputation. Their games are known to be "hard but fair", but this definitely isn't the case for Malenia.
Nowadays, I love fighting Malenia because I know the trick behind that one bullshit move and don't bring summons to give her easy health steal. I also know how to crush her poise and abuse crits to stunlock her. Doesn't mean the fight is well designed though.
