The only potential problem is that those who want a desktop that resembles the GNOME 2 series are likely to have tried the KDE 3 series some time ago, and disliked it. Yet Trinity KDE might be more acceptable now that you want an alternative to GNOME 3 -- and, as always, customization works wonders.
Xfce is the most popular of the lightweight desktops. Its general impression is of a stripped-down, faster version of the more recent releases in the GNOME 2 series. It even uses the GTK+ 2 toolkit for drawing windows, just as GNOME does. However, you may have to search for the configuration options, especially if you want icons on the desktop.
With the exception of the file manager Thunar, Xfce lacks first-class utilities, as well as GNOME's broad ecosphere of applications. In compensation, it runs both GNOME and KDE applications well, giving you the option to have the necessary support start as soon as you log in.
In case your video card does not have the hardware acceleration necessary for GNOME 3, a fallback desktop is available. You can start the fallback yourself at Applications -> System Settings -> System Info -> Graphics -> Forced Fallback -> On. This alternative closely resembles GNOME 2.32. Reconfigure so that you can have titlebar icons and desktop application launchers, and the resemblance is almost perfect.
You will notice some changes, such as the mercifully unobtrusive notifications and the ability to move to the chat window without your current window losing focus. However, these are small changes that are unlikely to affect your workflow in GNOME.
The only potential problem with the GNOME 3 fallback mode is that, sooner or later, it might be discontinued, particularly as the hardware acceleration on free video drivers improves. Yet even if that happens, you should still have a year or more in which to consider alternatives.
As anyone familiar with the range of free software desktops is aware, these are only the leading contenders for GNOME 3 replacements. I have deliberately not mentioned most of the available window-managers, particularly the tiled ones, because anyone who wants to recreate the experience of GNOME 2 would probably not be satisfied with them.
Which of the seven summarized here you choose depends on how closely you want to recreate the GNOME 2 experience, and what you expect in a desktop. GNOME 3's fallback mode has an obvious advantage, but some may be angry enough at the changes to move away from GNOME entirely.
Those who want to replace one fully-equipped desktop with another might consider Trinity or Xfce if they want little change. If they are more adventurous, then the latest KDE or Unity might be worth investigating. If greater speed sounds attractive, then Enlightenment, LXDE become possibilities. If you want to balance features and speed, then Xfce may meet your preferences.
Eventually, a fork of the GNOME 2 series may become available. It will not be EXDE, a tentative project that recently explored the possibility and has apparently rejected it, but one will probably emerge if enough people are interested. Meanwhile, since you are dealing with free software, you have no shortage of alternatives to explore.
ALSO SEE: GNOME vs. KDE: The Latest Round