This comes up quite a bit so I will write up a full list of differences and similarities at some point. I also think both borrow heavily from Lifeboats
There are similarities but also major differences. While they share a number of cosmetic similarities and actual mechanics, the gameplay is very different.
Crucially Mob Ties is about area control and playing cards in a 'take-that' style, which are used to kill off your opponents mobsters, voting occurs to make money, to elect a Don and occasionally to see who gets pinched by the police.
Where as Mall of Horror is a survival game that's focus is about movement and puts a greater emphasis on voting, much more akin to Lifeboats.
Some argue that the police in Mob Ties are the same as the Zombies in Mall of Horror. While it may look like this on paper, the police in Mob Ties are a mild irritant but the real harm comes directly from other mobsters, where as in Mall of Horror the zombies, their presence and moving around them is the core of the game. If the police pinch you in Mob Ties you get arrested and can simply pay your way out of jail... they don't eat you
I have Mob Ties but will definitely be buying a copy of Mall of Horror... been waiting an age for them to reprint it
. Both are worth owning, especially if you like negotiation games. This said whether owning both Lifeboats and Mall of Horror would be worth it is more difficult to say.
I think Mob Ties is better with 3 than Mall of Horror, simply because voting is not the core mechanic. We have a three player tournament on at the moment and do enjoy it although both are better with more players.
Rules for all three games are on bgg, in some form, and Mob Ties p&p can be downloaded here:http://www.hostage-entertainment-store.com/