I was expecting a reskin of the original Infectonator, but I was pleasantly surprised to find this not the case.
There is no longer a giant notification covering almost half the screen when an achievement is earned. The size has been greatly reduced, now no longer getting in the way of gameplay.
The replacement of the timer with a day counter was a good idea. While it changes little in the mechanics of the game, it significantly impacts the meta-game by allowing the player to take several different paths to upgrade progression, since it is no longer constrained by a need to clear the screen as quickly as possible.
The inclusion of a way for the virus to go through people is a welcome addition, and allows for less restrictive planning. However, it is more than a little overpowered. Once a player has the upgrade, they are almost unstoppable.
The increase in the price of upgrades is a small thing, yet rather significant. While the two most important traits are still raised to the same price as the rest, the least important factor was left unchanged, showing a clear effort at balancing the game was made, as opposed to simply raising the prices solely to make the game more difficult.
The music continues to be really good. While not as memorable or recognizable as the music from the original, it still manages to keep the tone of the game while successfully adding a Christmas theme to it.
A massive improvement to the original, keeping what made the game good, and fixing and tweaking what held the game back.