Lexus tends to name its car models using a fairly utilitarian
if somewhat opaque
naming scheme. Typically, the model names contain a two-letter model code and at times a three-digit engine code; as of mid-2003, their model line looks like the following.
The LS430 is labelled 'Prestige Luxury Sedan' on Lexus' documentation. I'll guess that the LS is Luxury Sedan. The current model sports a 4.3 liter V8 engine; the prior model (the LS400) had a 4.0 liter V8. This is the 'land yacht' model; big, squarish, luxurious and expensive. They are equipped with all manner of luxury amenities including navigation and entertainment systems, seat warmers, multiply-adjustable seats with memory systems, remote controls, yadda, yadda, yadda. Expect around 9 miles per gallon in city driving, but a surprisingly efficient 20-24mpg on the highway.
The GS series is available with two different engines. Yup, you guessed it, a 3-liter inline-6 or a 4.3-liter V8. Lexus claims the 'GS' stands for 'Performance Luxury Sedan.' I can't think of what the G might be except for 'General Purpose' (which is what car manufacturers have all started calling 'sport sedans,' whatever that means).
The ES used to be called the ES300, but they seem to have dropped the number since there's only one option. While they label it simply 'luxury sedan' let's be honest and call it what it is - the 'Economy Sedan' of the line. While much more plush than most other cars on the market - and with a price to match - it still looks rather small and spartan next to, say, its bigger sibling the LS430.
The IS is also a 3-liter inline engined sedan. It comes in three varieties, including the 'wagon' or 'SportCross 5-door.' I'm not sure what the I stands for (Intermediate?), but has traditionally meant the hatchback or extended utility sedan in the Lexus line.
Perhaps the most stand-out, the SC (Sport Coupe, or Sport Convertible) is a retractable-hardtop, two-place sports car with the same 4.3l V8 as the much heavier LS...meaning, of course, it Goes Real Fast(tm). But naturally, it does so on Lexus plush leather, with gadgets, etc. etc.
Now just the LX, this comes with a 4.7-liter V8. It's the mammoth 'SUV' of the Lexus line, and is known in its more utilitarian chassis form as the Toyota Land Cruiser. Big, boxy, and probably able to drive straight over any of the other models in the line-up. L for Luxury, X for...eXtreme? God, I hope not.
The 'mid-sized' SUV; the G is a smaller version of the LX.
Baby bro, the RX-330 is a small four-wheel-drive recreational/utility vehicle with the same inline-6 engine as the newer ES. It replaces the original RX300 in the Lexus stable.
I'll let others talk about the experiences of owning/driving these, save for the LS400. I was fortunate enough to be the caretaker of (note I do not say owner) of a 1996 LS400 for a couple of years. I still think it is probably the highest-quality, most comfortable car I've ever driven. For something that large and powerful, it drives extremely predictably; you're not going to pretend that you're Bobby Rahal or Jeff Gordon in this thing, but that's not the point. The point is that it contains a sitting environment that is roughly as comfortable as my living room if not more luxurious (leather seats, individual HVAC, Nakamichi stereo) - but it's a living room that moves at high speed. For highway travel, I have not yet been in a car that surpasses it for ride quality, soundproofing, and general relaxation. If the BMW sedans are built for the driver (as they claim) then this one is built for the passengers - of which the driver is one.