I don't like Arrest at all, I don't ever really consider it for my white decks. I dislike Reprisal as well, I don't have any decks that play it.
I think both are perfectly fine.
The issue I think is that both strike me more as SB cards. Well, I can see them being MD, but mostly in decks that can afford to really play with them.
Reprisal is actually a pretty good way of killing fatties at instant speed on the cheap. Biggest problem is how often the spell is going to be dead. I don't think running
Reprisal is bad, but I wouldn't run more than 1-2 copies MD. Even then, the card really works best when coupled with other effects that make it dead less often (like how my 5 color creature-less control deck uses the
effect on Obelisk of Alara to hit things both Obelisk and Reprisal are usually dead against).
Arrest is decent as well, although I do think it is a far cry from being the best removal in the format.
It does have it's advantages I will grant that. The biggest being that it is removal that doesn't send the target to the GY, which can be very relevant in a meta such as this where GY based strategies are powerful and common. It also has a few niche applications, like being an Aura for
Hero of Iroas and a permanent for
Pyxis of Pandemonium.
I think it has too many downsides to be considered really good.
Arrest is slow, both in cost (3 cmc) and in use (sorcery speed). It folds hard to decks that have methods of bouncing or sacrificing their own creatures. It is an Enchantment, meaning you not only have to worry about stuff like counterspells and protection effects (Gods Willing) blanking your removal, you have to worry about incidental Enchantment removal blanking your removal as well. It also doesn't do anything to stop triggered abilities, meaning it really doesn't do much to stop something like Talrand or Rabblemaster from doing exactly what they do to win games, accrue value.
I personally think both are better relegated to the SB unless you have a specific means to build around them (like Pyxis+Arrest for example), only coming in in matchups where you know they are going to provide sufficient value.