The breakpoints on this depend significantly upon whether or no you're able to buy off the LA from it. No matter what, though you never want to take the fifth level, since it's worse than a level of commoner.
Level 1
Undead immunities. Incorporeality/Etherealness. Fly speed. Immunity to sundering/disarming from your ghostly equipment.
Probably the most significant change in your character. An absolute gamebreaker at low levels, since you're immune to all nonmagical attacks, a significant fraction of magical attacks, and have a 50% miss chance against almost anything that could actually harm you. The biggest downside here is the low hp (if you're playing a beatstick), and the difficulty in actually attacking. You may be reduced to meleeing with 80 gp
serren arrows.
For a more advanced character, this is basically the [functional at high levels] subtype. You get immunity to most save-or-die spells, the ability to deal with a significant amount of "screw you" effects, excellent mobility, and a decent amount of defenses. Yeah, the HP isn't great (unless you get killed by a dread necromancer on a desecrated altar), but at high levels HP matters less anyway.
You also get cha to AC, which is pretty neat.
Level 2
The charisma bonus and turn resistance are OK. The biggest draw here is the lesser ghost power. Let's run through what options you have.
Corrupting Touch (Su): An inauspicious start to our ghost powers. You gain the ability do deal d6 damage with a touch attack. You know who else can deal d6 damage with a touch attack? Level one warlocks, that's who. And they can do it at range. Suck it.
Frightful Moan (Su): On the one hand, this has a decent DC, and panicking your enemies is a great debuff. On the other hand, it's sonic, necromantic, mind affecting, and a fear effect, and if they save once they're immune for 24 hours. Stupidly easy to counter, but powerful if you can land it. Averages out to mediocre once you're outside of very low levels.
Telekinesis (Su): My favorite of the lesser abilities. It has utility. It has battlefield control. It's the best damage dealing spell in the game. Your minimum CL for this is 12, and if you violent thrust big-ass crossbow bolts or sianghams you can easily deal 4d6 on each weapon. Coat them in drow poison, since rendering your opponent unconscious is as good as killing him. Or go for a debuff combo platter, and hurl a flask of torchbug paste, an eggshell grenade(dust), a net, a tanglefoot bag, and a lasso, and then follow it up with weaponry. Remember, mirror images will die if they get damaged even by the splash from an acid flask - if your first two attacks remove concealment and mirror images, you have a decent chance of actually landing the other ten.
The nice thing is, you can scale your use of telekinesis based on the campaign's power level. In a very high power world, you can break out the colossal+++ size categories from epic, while in a low power world you can just shoot daggers or miscellaneous bric-a-brac. In one particularly silly game, I hit enemies with bars of solid gold, just to prove I
could solve all my problems by throwing money at them.
Level 3
A few more skill bonuses. And Rejuvenation.
Rejuvenation is great. First, it makes you immune to death once you hit fifteenth level. This limit was carefully chosen by WoTC so that it'd normally be the capstone of a ghost PC (something 15/ghost 5). There are like two or three prestige classes or obscure abilities (like hunter of the dead) that can overcome rejuvenation - but that's it.
My suggestion for this ability is to carry around a Phaant's luckstone (ghostwalk) to get a reroll if it fails, or (if taint is being used) pick up the Surge of Malevolence feat for a +9 on one check/day. That makes you immune to death at level 6, which I think you'll agree is pretty nifty.
I will admit that there's a 2d4 day time period while you're out of commission. That actually makes it more likely your DM will allow it, since you can point out that there's real consequence for losing fights, while still providing everyone with TPK immunity.
Level 4
More charisma, more skills, more turn resistance. Most importantly, greater ghost powers. Here's a quick rundown of those.
Corrupting Gaze (Su): A gaze attack with a range of 30 feet. Deals 2d10 damage and d4 cha damage. It's a fort save, which isn't so good. Worse damage than horrific appearance, but at least you can turn it off.
Draining Touch (Su): Look closely at this ability. That's right, you add your strength modifier to your ability damage rolls for this against ethereal opponents. And you can hit any ability score you select. And ethereal in this case is referring to opponents who share a plane with you (since ghosts start off ethereal), so if you planeshift to the material plane and bulk up... can we say d4+stupid ability damage to your opponent's lowest stat? You can punch the stupid right into somebody. Oh, and to add insult to injury, you heal 5 hit points when you do it.
Horrific Appearance (Su): Anyone living in 60 feet that can see you takes d4 damage to every physical stat if they fail a fort save. Hits every round until they save. Nasty. Unfortunately, you can't turn it off, which makes it difficult to play well as a team.
Malevolence (Su): Like Magic Jar without the jar. Like Magic Jar without the SR. You want to cruise around in a golem's body? I thought so.
Or you can take the two lesser powers that aren't telekinesis if you're lame.
Level 5
Never take this level. Ever.
Note that the ghost savage progression, like the other web ones, is somewhat special - you
don't have to take the whole thing at once
Characters are not required to complete all the levels of a given template class in uninterrupted succession. For example, a character who takes a level of wereboar could then take a level of fighter and a level of rogue (or any other combination of other class levels) before taking another level of wereboar. A character must still take the first level of wereboar before taking the second, just as with a normal class.