- Humans are more vulnerable
FPS games are in essence spatial manipulation games. You input changes to the world around you in order to achieve a goal. As such, one of the most important skills in an fps is maneuverability. An opponent with greater maneuverability gets to manipulate the world more than a less maneuverable opponent. One of the main consequences of this is that they can set the engagement distance more easily, and determine when combat ceases. This is a crucial underlying problem in tremulous because humans can't break off the fight unless they kill the alien, or the alien retreats. This lack of maneuverability and control favors a more conservative style by the humans, and a more aggressive approach by the aliens.
- Structures cannot defend themselves
In tremulous, all bases can, with enough time, be destroyed by one alien (or human, though they generally have to worry about ammo more). They are in constant need of babysitting as they cannot defend themselves effectively. As stated before, humans have less maneuverability, and thus less ability to react to changing conditions on the map. A surprise attack by the aliens can be unopposed for 15-20 seconds while the humans scramble back to base. An attack by humans rarely lasts that long before they are confronted. This makes it harder for humans to push out since when they leave the base they are simply putting out an invitation for the aliens.
- Humans are more base-dependent than aliens
As a human, the main consideration you have to account for is health. For every encounter, you trade some health and ammo and resources for expected future health and ammo (credits). When the perceived loss in resources (eg. dying) falls below the expected return, players attempt to break engagement and replenish these sources. For humans, this often requires a trip back to the base upwards of 30 seconds round trip (10 seconds to and from, and 10 seconds in-base). During this time, humans cannot defend the perimeter and they cannot gain credits. Aliens, on the other hand, can simply fall back to the previous room and regenerate hp, or go to an egg. This process can take less than 20 seconds (5 seconds to and from, and 10 seconds healing). During this time, they are close to the front line which they can defend if need be and earn credits in the process. This ability for aliens to constantly reinforce lets them hold a front line much further up than the humans.
Lets look at the implications of the new res system on these factors. In the first factor, humans are still more vulnerable. In the second, the humans base is still more vulnerable. In the third, the humans are still as base dependent. The humans must now have good map control, even though the underlying problems leading to lack of human map control have still not been addressed. As we have seen, this leads to even more alien wins and human losses.
Second, the new system does not actually promote aggressiveness. It simply increases the number of defenses available, making it harder to win the game. In Risk, for example, neither the defenders nor the attackers have an advantage. This leads to long games where the only way to win it by playing risk cards. However, these simply add more units and simply increase a player's "hit points." In addition, there is an incentive to play these cards as late as possible as you get more armies that way. These systems lead to long, boring games, which does not seem to be what you had in mind.
For the second point, there is nothing you can do, as making structures more powerful would decrease the ability of first stage aliens to make any sort of dent. However, there are ways to mitigate the first and last reasons. The last can be fixed by giving humans regenerating health and not aliens. Regenerating ammo for energy weapons could also work as a cool thing that would extend human range. In terms of the first point, I believe that the dev team does not want to increase human ability to maneuver in combat. Excluding that, there are several ways to increase humans' passive mobility. Teleporters have been used before and can greatly increase a team's ability to react. A speed boost ability could also be included (an item that would give the humans 2 speed, but could not be used while in-combat). Overall, however, the main relationships should be rethought to mitigate the causes of camping, or make camping fun for both teams and embrace the result.