Our cars have hydraulic engine mounts, which do a much better job of isolating the chassis from engine vibration, and as a result, let the engine/gearbox move around quite a lot. If you watch any in-car video (some links are posted in this forum) you will see a lot of movement as the engine is loaded and unloaded. If you can push on the shifter (in gear) and it feels solidly connected, you are OK. If it rattles around, have it checked.
As theirishgonzo said, you should not push on the shifter while you are driving. Doing that holds the shift fork against the synchro, and will cause wear and other bad things inside the gearbox. Both hands on the wheel, except when shifting ! OK, there are other exceptions.....never mind.
Most people can pull things easier than they can push them, as the bicep is typically stronger than the tricep, and the leverage is better, so the 1/2 detent should feel softer than the 5/R detent. Of course, inhibiting a 3-R shift is more important than inhibiting a 3-2 or even a 4-1 shift, so the 5/R detent may in fact be stiffer. Maybe I'll measure it.