The game doesn't even start for me. I always get the error message:

Unable to preload the following plugins: ScreenSelector.so

My system:

System:    Host: home Kernel: 4.9.0-7-amd64 x86_64 (64 bit)
           Desktop: Openbox 3.6.1 Distro: BunsenLabs GNU/Linux 9.5 (Helium)
Machine:   Device: laptop System: LENOVO product: 64758N1 v: ThinkPad T400
           Mobo: LENOVO model: 64758N1
           BIOS: LENOVO v: 7UET79WW (3.09 ) date: 10/13/2009
Battery    BAT0: charge: 56.4 Wh 99.5% condition: 56.7/56.2 Wh (101%)
CPU:       Dual core Intel Core2 Duo P8600 (-MCP-) cache: 3072 KB 
           clock speeds: max: 2401 MHz 1: 1600 MHz 2: 1600 MHz
Graphics:  Card: Intel Mobile 4 Series Integrated Graphics Controller
           Display Server: X.Org 1.19.2 drivers: modesetting (unloaded: fbdev,vesa)
           Resolution: 1440x900@60.26hz
           GLX Renderer: Mesa DRI Mobile Intel GM45 Express
           GLX Version: 2.1 Mesa 13.0.6
Audio:     Card Intel 82801I (ICH9 Family) HD Audio Controller
           driver: snd_hda_intel
           Sound: Advanced Linux Sound Architecture v: k4.9.0-7-amd64
Network:   Card-1: Intel 82567LM Gigabit Network Connection driver: e1000e
           IF: enp0s25 state: down mac: 00:24:7e:e0:f1:d2
           Card-2: Intel PRO/Wireless 5100 AGN [Shiloh] Network Connection
           driver: iwlwifi
           IF: wlp3s0 state: up mac: 00:26:c6:40:f7:ec
Drives:    HDD Total Size: 160.0GB (41.6% used)
           ID-1: /dev/sda model: WDC_WD1600BEVS size: 160.0GB
Partition: ID-1: / size: 28G used: 5.3G (21%) fs: ext4 dev: /dev/sda1
           ID-2: /home size: 117G used: 55G (50%) fs: ext4 dev: /dev/sda6
           ID-3: swap-1 size: 2.04GB used: 0.15GB (7%) fs: swap dev: /dev/sda5
Sensors:   System Temperatures: cpu: 40.0C mobo: 36.0C
           Fan Speeds (in rpm): cpu: 1824
Info:      Processes: 154 Uptime: 1 day Memory: 1412.4/1898.5MB
           Client: Shell (bash) inxi: 2.3.5

try to run it with 

./RotT.x86_64 -screen-fullscreen 0

Unfortunately, it didn't work out. My output:

Preloaded 'ScreenSelector.so'
Unable to preload the following plugins:
    ScreenSelector.so
Logging to /home/rothom/.config/unity3d/Catmic/Return of the Tentacle/Player.log

The ScreenSelector.so error seems not to the fatal one, because i've have it also on my system all the time without any problems starting the game.

Just have a look at the Readme.txt in the game folder, there are a few start options for debugging.

My worst expectation is that your chipset GFX doesn't meet the minimal requirements, but that can only be answered by the game devs. Maybe it's helping them if you can post the output from 'glxinfo -B'

My glxinfo -B output:

name of display: :0
display: :0  screen: 0
direct rendering: Yes
Extended renderer info (GLX_MESA_query_renderer):
    Vendor: Intel Open Source Technology Center (0x8086)
    Device: Mesa DRI Mobile Intel® GM45 Express Chipset  (0x2a42)
    Version: 13.0.6
    Accelerated: yes
    Video memory: 1536MB
    Unified memory: yes
    Preferred profile: compat (0x2)
    Max core profile version: 0.0
    Max compat profile version: 2.1
    Max GLES1 profile version: 1.1
    Max GLES[23] profile version: 2.0
OpenGL vendor string: Intel Open Source Technology Center
OpenGL renderer string: Mesa DRI Mobile Intel® GM45 Express Chipset 
OpenGL version string: 2.1 Mesa 13.0.6
OpenGL shading language version string: 1.20
OpenGL ES profile version string: OpenGL ES 2.0 Mesa 13.0.6
OpenGL ES profile shading language version string: OpenGL ES GLSL ES 1.0.16