There are currently three engines in use in the TeX community: pdfTeX, XeTeX and LuaTeX and they all serve an audience.
The pdfTeX engine is a stable extension to TeX that has eTeX on board as well as a few extensions. It provides hz and protruding and supports advanced PDF output. It is fast and reliable and sort of frozen with respect to functionality. It will stay around for ever but has only limited provisions for dealing with OpenType fonts.
Then there is XeTeX which supports Unicode as well as OpenType by means of third party libraries. It integrates nicely into the current infrastructure and support from macro packages is easy as there are no fundamental changes in interfaces and functionality. It uses the eTeX r2l typesetting while LuaTeX uses the Omega (Aleph) method. Support from macro packages does not demand changes in the core.
The LuaTeX project uses a different approach. Instead of using libraries it provides an extension mechanism. This keeps the program independent and permits the flexibility that we like so much. However, it comes at a price. First of all LuaTeX does not have the performance of its cousins, although for instance the average ConTeXt MkIV run can be faster in LuaTeX. LuaTeX also demands extensive support at the macro level if you want to profit from its benefits. Just adding some support for scripting is nice but the power of LuaTeX only shows when it's tightly integrated. This integration is also needed in order to provide macro users some stability as most of them are no TeX programmers. If such integration is not what you want, you might consider sticking to the other engines as there are no real advantages to using LuaTeX then.
having a more-modern language for scripting? I remember that tikz (a library for vector graphics) had to emulate some floating point math because it just wasn't supported by TeX (which meant when I wrote my thesis, my macbooks fans were going through the roof).
There are currently three engines in use in the TeX community: pdfTeX, XeTeX and LuaTeX and they all serve an audience.
The pdfTeX engine is a stable extension to TeX that has eTeX on board as well as a few extensions. It provides hz and protruding and supports advanced PDF output. It is fast and reliable and sort of frozen with respect to functionality. It will stay around for ever but has only limited provisions for dealing with OpenType fonts.
Then there is XeTeX which supports Unicode as well as OpenType by means of third party libraries. It integrates nicely into the current infrastructure and support from macro packages is easy as there are no fundamental changes in interfaces and functionality. It uses the eTeX r2l typesetting while LuaTeX uses the Omega (Aleph) method. Support from macro packages does not demand changes in the core.
The LuaTeX project uses a different approach. Instead of using libraries it provides an extension mechanism. This keeps the program independent and permits the flexibility that we like so much. However, it comes at a price. First of all LuaTeX does not have the performance of its cousins, although for instance the average ConTeXt MkIV run can be faster in LuaTeX. LuaTeX also demands extensive support at the macro level if you want to profit from its benefits. Just adding some support for scripting is nice but the power of LuaTeX only shows when it's tightly integrated. This integration is also needed in order to provide macro users some stability as most of them are no TeX programmers. If such integration is not what you want, you might consider sticking to the other engines as there are no real advantages to using LuaTeX then.