The Combat Upgrade changed a lot. Here is a collection of important info on the changes.

Profession Roles

Don't expect a single player game. If you insist on going after the big game, you'll need company.
Find or form a group. Make sure it's varied. The new profession roles should be utilized:

• Ranged fighters will deal damage
• Melee fighters (tanks) will keep the the opponents from rushing the ranged fighters
• Crowd Control Characters will make sure the opponents won't do too much damage to the tanks
• Healers will keep players that take damage from dying

The new roles of combat professions

Respecs were introduced to make up for the changes made to the combat professions. - Characters that were created prior to the CU has been given the opportunity to respec, meaning to trade their skills into different skills in order to try out other professions, in case they no longer like the profession after the CU changes.

Buffs

Doctor buffs, in the sense that the veteran players know them, are gone. Doctors can still buff, but the effects are less noticeable, and a bit different.
Consequently, a lot of doctors left the profession, and those that didn't are not located in Coronet any longer, as doctor is now a combat profession. You may find a few buffing and/or healing in Dantooine Mining Outpost.

• Short term buffs will modify the health value no more than 20%.
• Long term buffs will modify the health value no more than 10%.

Entertainer buffs have changed as well. Players no longer have secondary stats, so instead of buffing these, entertainers can give you an inspiration buff. There are several types of Inspiration Buffs:

1. Passive buff - The general inspiration buff: Watch/listen to any entertainer. - 10% xp and fp bonus while buffed.
2. Artisan buff - The general crafting buff: Ask for this. - 12% xp bonus, 1% resource quality bonus, 5% assembly and experimentation bonus while buffed.
3. Entertainer buff - For entertainers: Ask for this. - 12% xp bonus, allows the use of more advanced (by one level) props and instruments while buffed.
4. Musician buffs - For Architect, Droid Engineer, Weaponsmith, Shipwright or Armoursmith: Ask for the profession you want. - 15% xp bonus, 2% resource quality bonus, 10% assembly and experimentation bonus while buffed.
• - For Dancer: Ask for this. - 15% xp bonus, allows the use of more advanced (by two levels) props and instruments while buffed.
5. Dancer buffs - For Chef, Tailor or Bio-Engineer: Ask for the profession you want. - 15% xp bonus, 2% resource quality bonus, 10% assembly and experimentation bonus while buffed.
• - For Merchant: Ask for this. - 15% Merchant xp bonus and 20 point hiring skill bonus while buffed.
• - For Image Designer: Ask for this. - 15% ID xp bonus and 50 charge hologenerators while buffed.
• - For Musician: Ask for this. - 15% xp bonus, allows the use of more advanced (by two levels) props and instruments while buffed.

Battlefatigue has been removed from the game.

Food buffs are also changed, and due to the reduction of doctor buff effects, they are more relevant now than before.
The type of effect you get from a certain food may no longer be the same as it used to be.

The Secrets of Good Eating - A guide to post-CU foods.

Combat and the Combat Level

The Combat Upgrade also introduced the Combat Level for players, and similar levels for mobs.
This is a system designed to focus your combat on the targets that are "interesting" to you. No more grinding quenkers or squills for xp...

If you kill a mob that is 5 or more levels below you, you will only get 1 xp for the kill.
If you kill a mob that is around your level, you get full xp.
If you kill a mob that is 5 or more levels above your level... You are a pro. That is very hard to accomplish solo.

Your combat level depends on the combat skills you have learned. The more combat skills, the higher your level.
At master elite, e.g. master rifleman, you are combat level 54...
The highest level reacheable is CL80. There are mobs with even higher levels, for groups of high-level players.

You can read more about what will influence your combat level here

A friday feature on combat after the CU

Armor

To complement the new roles, each combat profession gets access to a set of armor types. They can only wear armor of these types, and they need at least the novice skill from their (elite) profession, in order to wear it:

Reconnaissance Armor - BioEngineer¹, Pistoleer, Rifleman, Smuggler
Ubese, Tantel, Mabari, Kashyyykian Ceremonial, Ithorian Guardian, Marine Rebel (Factional), Scout Trooper (Factional)
Bonus: +1000 Energy ... Penalty: -1000 Kinetic

Battle Armor - Carbineer, Combat Medic, Creature Handler, Doctor, Fencer, Pikeman, Ranger, Swordsman
Padded, Marauder, Bone, Kashyyykian Black Mountain, Ithorian Defender, RIS (Quest), Rebel Battle (Factional), Stormtrooper (Factional)
No bonus, no penalty.

Assault Armor - Bounty Hunter, Commando, Squad Leader
Chitin, Composite, Kashyyykian Hunting, Ithorian Sentinel, Mandalorian (Quest), Rebel Assault (Factional), Shock Trooper (Factional)
Bonus: +1000 Kinetic ... Penalty: -1000 Energy

Teras Kasi Artist is a damage avoiding profession, that is played without armor.
¹) BioEngineers only receive hindrance mitigations equal to "basic" core armor.

The protection varies as you can see from the table below. But the max unlayered protection will always be 6000, there will then be modificers or penalties for the different types.
All armor in a given class can have the same stats regardless of armortype (Chitin ~ composite, e.g.) - only appearance changes!

The effective protection of armors has changed as well.
Before the CU, this was measured in percentages. After the CU there is an equivalent, but the cap is "60%" and the closer you get the less extra % you get from the next protection point. This is illustrated below:

1000 = 10.5%
2000 = 20.0%
3000 = 28.5%
4000 = 36.0%
5000 = 42.5%
6000 = 48.0%
7000 = 52.5%
8000 = 56.0%
9000 = 58.5%
10000 = 60%

More info on armor

Weapons

You now need more than skills to wield a weapon - you need certain Combat Levels (CL) as well.

CL - Weapon available